Structure-Augmented Reasoning Generation
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• 2506.08364 • Published
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doc1 | Abstract Gaucher disease, an autosomal recessively inherited lysosomal storage disorder, results from biallelic mutations in the GBA1 gene resulting in deficient activity of the enzyme glucocerebrosidase. In Gaucher disease, the reduced levels and activity of glucocerebrosidase lead to a disparity in the rates of formation and breakdown of glucocerebroside and glucosylsphingosine, resulting in the accumulation of these lipid substrates in the lysosome. This gives rise to the development of Gaucher cells, engorged macrophages with a characteristic wrinkled tissue paper appearance. There are both non-neuronopathic (type 1) and neuronopathic (types 2 and 3) forms of Gaucher disease, associated with varying degrees of severity. The visceral and hematologic manifestations of Gaucher disease respond well to both enzyme replacement therapy and substrate reduction therapy. However, these therapies do not improve the neuronopathic manifestations, as they cannot cross the blood–brain barrier. There is now an established precedent for treating lysosomal storage disorders with gene therapy strategies, as many have the potential to cross into the brain. The range of the gene therapies being employed is broad, but this review aimed to discuss the progress, advances, and challenges in developing viral gene therapy as a treatment for Gaucher disease. Keywords: Gaucher disease; gene therapy; vector; AAV; therapeutics; murine models 1. Introduction 1.1. Gaucher Disease Gaucher disease (GD) is a very heterogeneous disorder with varying clinical manifestations and severity. Classically, GD has been classified into three types, determined by the presence (or absence) and varying degree of neurological symptoms. Type 1 (GD1), or non-neuronopathic GD, is the most common form in the Western world and is enriched in the Ashkenazi Jewish population [1]. Systemic manifestations of GD frequently include hepatosplenomegaly, thrombocytopenia, anemia, and bone involvement, although some patients exhibit few or no symptoms of the disease. Acute neuronopathic type 2 (GD2) is the most severe form of the disease, with patients exhibiting rapid onset and progression of symptoms within the first few months of life, typically succumbing to the disease between infancy and age four. Type 3 (GD3), or chronic neuronopathic GD, presents with relatively milder neurological symptoms but a wider range of phenotypes. Neurological manifestations in neuronopathic GD (nGD) can range from slowed horizontal saccadic eye movements to myoclonus, ataxia, and seizures [2,3,4]. Due to its variable manifestations and overlapping features with other diseases, the diagnosis of GD can be difficult and even missed in those with milder or later-onset presentations of the disease. Making a timely diagnosis can be critical as, in many instances, there is an optimal time to begin treatment to avoid irreversible damage [5,6]. Treatment with the current therapies can be integral for reversing or preventing hematological and visceral involvement as well as improving patients’ quality of life. 1.2. Approved Therapies for Gaucher Disease Enzyme replacement therapy (ERT) is the first-line treatment for GD in patients of all ages. Current ERT for GD involves the administration of exogenously infused recombinant glucocerebrosidase to compensate for its deficiency [7]. There are three FDA-approved recombinant enzymes for Gaucher disease (imiglucerase, velaglucerase alfa, taliglucerase alfa), all of which are administered intravenously and appear to have similar efficacy [5]. Alleviation and reversal of most non-neuronopathic symptoms can be successfully achieved in most patients after an optimal dosage for the individual is determined [5,8]. Long-term cessation of enzyme replacement therapy often results in the reemergence of disease manifestations, albeit reversibly, so long as therapy is restarted in a timely fashion [8,9]. ERT is considered very safe, with reported side effects rarely warranting discontinuation of treatment [10]. However, despite its efficacy, ERT can be prohibitively expensive for many patients, limiting its availability for those who are unable to afford it, especially in developing nations [5,9,11]. Some patients cannot tolerate ERT due to poor venous access, allergy, or, in rare instances, hypersensitivity [11]. Coordinating infusions, which are typically administered in clinics, hospitals, or by home infusion nurses, can be challenging—an issue that was highlighted during the SARS-CoV-2 pandemic [9,12,13,14]. Furthermore, the recombinant enzyme is unable to cross the blood–brain barrier (BBB), rendering it ineffective for the neurological manifestations of GD observed in GD2 and GD3 [8,11,15]. For adults, including those unable to access or tolerate ERT, oral substrate reduction therapy (SRT) is a second option for the treatment of GD. While enzyme replacement therapy seeks to restore deficient glucocerebrosidase levels, substrate reduction therapy inhibits the rate of synthesis and subsequent accumulation of glycosphingolipid substrates [16]. There are currently two glucosylceramide synthase inhibitors approved as SRT for GD. Miglustat was the first SRT available [17]; it diffuses widely and rapidly into tissue and can cross the BBB, but many side effects have been reported [18]. A randomized controlled trial in 30 patients with GD3 failed to show significant neurological improvements following miglustat treatment [19]. The second SRT approved for GD, eliglustat tartrate, has greater efficacy and milder side effects than miglustat and is thus the most commonly used SRT [5,15,20]. However, eliglustat does not cross the BBB and is not approved for neuronopathic GD [21,22]. Dosing for eliglustat is dependent on the patient’s CYP26 metabolism, and the therapy is not indicated for those who are ultra-rapid CYP26 metabolizers or have any degree of hepatic impairment [5,23]. Currently, children are excluded from the therapeutic indications for SRT—an undesirable aspect given the importance of early treatment to prevent irreversible damage and developmental complications [24]. Furthermore, in contrast to ERT, the side effects observed with SRT are notably more severe, with a greater percentage of patients ending treatment as a result [5,25,26]. SRT is also still quite expensive–another barrier for patients worldwide [27]. A brain penetrant SRT, venglustat, is currently in clinical trials [28]. While current therapies for GD are highly effective and life-changing for many patients, they entail high costs and must be taken regularly for the rest of a patient’s life. Although other treatments such as bone marrow transplant are practiced in countries unable to afford ERT or SRT, these methods are considered less effective and carry a higher risk of complications [27,29]. Additionally, no current therapies are effective against neurological manifestations of GD. Thus, there is a critical, unmet need for a more affordable solution for the treatment of GD that is also capable of improving the neuronopathic aspects of the disease. Gene therapy holds potential as a curative therapy for GD that could address the shortcomings associated with current treatment options. 1.3. Gene Therapy For many decades, gene therapy has been heralded as a promising therapeutic strategy for the treatment of different inherited disorders, including lysosomal storage disorders (LSDs). The ultimate goal of gene therapy is to modulate or manipulate the expression of genes in order to achieve a therapeutic effect in genetic disorders. This enables the introduction of healthy copies of a gene to replace diseased copies, the disruption of the functionality of diseased genes (through transcriptional or translational modifications), or the introduction of a novel gene for a therapeutic effect [30]. In gene therapy, the cargo (therapeutic gene) is delivered via a carrier (vector) to targeted cells. These vectors can be grouped broadly into viral and non-viral approaches. Non-viral gene therapy methods include synthetic polymers and natural polymers, which take advantage of organically derived cellular components [31,32]. Non-viral modalities offer relatively low immunogenic responses and are not limited by the size of the DNA inserts [33]. However, the poor selectivity and limited efficiency of genetic material transfer with non-viral gene therapy methods make viral gene therapy more attractive for therapeutic and clinical applications. Viral gene therapy uses vectors that are highly selective within target tissues, while also being versatile enough to differentiate amongst cells in different stages of the growth cycle [33]. Viruses that have been modified for gene therapy include retroviruses, adenoviruses, lentiviruses, and adeno-associated viruses (AAVs) [33]. Retroviruses rely on modifications of their long terminal repeats to deliver transgenes to the genome in a random integration format. However, they are associated with potential immunogenic and toxicity complications, posing safety concerns [34]. Adenoviruses were initially considered as a viable viral vector template due to their generally non-lethal properties when found in nature. However, the adenovirus may trigger a strong inflammatory response when injected into the host [35]. There are many adenovirus serotypes, but historically, group C human serotypes 2 and 5 have primarily been used in gene therapy, as they have potent transduction capacity [36]. The immunogenic risk of adenoviruses remains the primary limitation to their use as a gene therapy vector despite ongoing research [37]. Adeno-associated viruses (AAVs) offer additional advantage with respect to immunogenic protection when compared to other viral vectors [34]. Although other viral vectors have been modified to prevent infection, AAVs have an additional level of separation from infectivity that makes them attractive candidates for gene therapy. The reliance of AAVs on helper viruses precludes an adaptive response, as they have been shown to be apathogenic in humans, an important distinction to consider when comparing them to other viruses that may have previously caused infection in patients and thus trigger a strong immune response in gene therapy [38]. Twelve AAV serotypes with at least one hundred variants have been identified [39]. Adeno-associated viruses contain a small single-stranded linear genome that allows for modifications and inserts. The heterogeneity amongst these variants enables modified AAV vectors to target multiple tissue types with high infectivity. While some serotypes appear to be specific to certain tissue types, the targets of other serotypes remain unclear [40]. Currently, tissue-specific promoters in conjunction with machine learning techniques are being used to engineer more target-specific AAVs [41]. 1.4. Benefits of AAV Vectors in Gene Therapy The relatively small AAV genome is flanked on either side by 145 nucleotide inverted terminal repeats (ITRs), which are amenable to small therapeutic inserts of desired genes [42]. In gene therapy applications, the AAV genome is replaced with the desired foreign DNA, which is selectively designed for expression in tissues of interest. These DNA inserts encode specific transgene cassettes containing the therapeutic DNA, a regulatory sequence, a promoter, and a polyadenylation (poly(A)) signal, which ensure the appropriate mRNA processing and translation [43]. The variability amongst the many AAV serotypes further improves tissue-specific targeting and transduction into cells. The specific mechanisms for transduction into the cellular genome differ depending on the selected serotype and vector design but can include random integration of the vector genome into chromosomal regions [44] and episomal transgene expression [45]. Additionally, the safety profile of AAVs is associated with a lower immunogenic response and improved outcomes for transduction of the target gene into desired tissues and cells when compared to adenoviruses and retroviruses [34,46], suggesting that AAV is a more optimal viral gene therapy option for genetic diseases. Many LSDs, including GD, have neurological involvement. Gene therapy offers a special advantage for neurological disorders, as many of the vectors have unique properties that allow them to permeate the BBB. AAV vectors are efficient and highly selective at transducing tissues throughout the nervous system when used in conjunction with cell-type-specific promoters and enhancers [47,48], enabling their delivery to affected brain regions. AAVs can deliver therapeutic proteins, antibodies, micro-RNAs, or precise DNA insertions and deletions to alter the genomic profile of the host cells [49]. Pre-clinical studies have suggested that direct intravenous delivery of the AAVs may be as efficacious in reversing neuronopathic phenotypes as intracerebroventricular injections exclusively targeting the central nervous system (CNS) [50]. Furthermore, several previous and ongoing clinical trials offer a cautiously optimistic view of the therapeutic potential of AAV vectors for the treatment of neurological disorders [51], supporting their safety in a clinical setting and their overall efficacy. It has also been observed that recombinant adeno-associated viral vectors are less immunogenic in all tissue types (including neuronal) than adenoviral vectors [52,53,54]. These clinical trials support the safety of AAV gene therapy in the treatment of heritable disorders and neurological disorders, making it a reasonable therapeutic approach for GD. 2. Current Progress in Gene Therapy for Gaucher Disease 2.1. Historical Overview While there are no FDA-approved gene therapy treatments for GD presently, there has been significant interest in this field spanning several decades, including work conducted with different murine models and viral vectors. Several studies have established a historical precedent demonstrating promise for GD as a viable candidate for gene therapy. Choudary et al. [55] were among the first to explore gene therapy for GD and successfully induced the expression of human glucocerebrosidase in mammalian cells via retroviral gene transfer. However, the expressed enzyme was inactive and did not rescue GCase levels. Shortly after, the successful transplantation of transfected bone marrow cells into murine models with recovery of macrophage and central nervous system microglia was reported [56]. Schiffman et al. provided support for the efficacy of retrovirally transduced bone marrow transplantation in mice with long-term survival through repeated injections of transduced stem cells [57]. In 1997 and 1998, three separate groups performed clinical trials to assess the developing technology. Schuening et al. introduced peripheral blood repopulating cells that had been transduced with a retroviral vector to patients. However, they were unable to produce successful engraftment of transduced cells [58]. In 1998, Dunbar et al. demonstrated long-term efficacious engraftment of infused gene-marked cells, but they were unable to show improved GCase activity in patients [59]. Barranger et al. transduced modified CD34+ cells into recipients and were able to observe sustained enzyme production in one patient for at least nine months [60]. These reported levels were sufficient for the patient to be weaned off ERT, but after 27 months, enzyme levels decreased and the patient had to resume infusion therapy. Several of these early studies supported the use of viral gene therapy, while cautioning about possible safety concerns related to potential oncogenic and immunogenic side effects of the therapy [61]. The shortcomings of these clinical trials supported the need for more vigorous pre-clinical studies. The scope of this review was focused on describing the potential efficacy of different viral vectors in vivo for gene therapy for GD. We evaluated the data presented in previous studies based on the murine models used to determine feasibility of the gene therapy treatments and their translatability, and the vector constructs and routes of administration to understand their efficacy and selectivity to certain tissue types (Table 1). Table 1. A summary of the pre-clinical gene therapy studies for Gaucher disease. 2.2. Murine Models Following the unsatisfactory clinical results of ex vivo gene therapy for GD, subsequent studies turned their focus to in vivo methods. However, animal research for GD has persistently been hindered by a lack of an appropriate animal model that accurately recapitulates the phenotypes observed in humans [71,72]. The feasibility of in vivo gene therapy for GD was first demonstrated in non-Gaucher BALB/c and C57Bl/6J mouse models, which established the capability of viral vectors to produce therapeutic and supraphysiological levels of GCase in serum and Gaucher-affected tissues [62,64,65]. Marshall et al. also used an artificially induced murine model of GD by treating BALB/c mice with conduritol-β-epoxide (CBE) and glucocerebroside-containing liposomes to inhibit GCase activity and increase glycosphingolipid levels, respectively. These mice accumulated GluCer in the lysosomal compartments of liver macrophages (Kupffer cells), effectively replicating one of the biological hallmarks of GD. The group demonstrated that gene transfer-induced secreted GCase could localize to Kupffer cells despite being unmodified and that it had a longer half-life than the modified enzyme administered in ERT. Successful targeting of GCase delivered to the macrophages efficiently cleared GluCer accumulation in the liver, confirming that GD is a viable candidate for in vivo gene therapy [62]. Despite the relative ease and low cost associated with generating the CBE mouse, it is ultimately a non-genetic model that is not sufficient for evaluating the efficacy of gene therapy in patients. Furthermore, it can be a rather variable model, as symptom presentation is largely dependent on CBE dose, length of treatment, and age and strain of the mouse [73]. As such, more accurate pre-clinical studies of in vivo gene therapy for GD required a genetic murine model that displayed a consistent phenotype. The development of the D409V/null mouse model by Xu et al. in 2003 allowed for further investigation into this therapeutic strategy [63,66,74]. While this GBA1 variant is not commonly encountered in patients with GD, mice with the genotype D409V/null exhibited a >94% reduction in GCase activity, accumulation of glycosphingolipids, and abnormal storage cells in visceral tissues. D409V/null mice appeared to have normal behavior, fertility, and lifespans. No neurological manifestations were observed and, hence, it best modeled mild, non-neuronopathic GD [74]. However, memory deficits associated with the accumulation of α-synuclein were observed as these mice aged [75]. This finding could confound the use of this mouse line in gene therapy studies by introducing additional symptoms associated with pathologies that the vectors are not designed to treat. Previous attempts to generate a complete knockout of Gba1 in mice resulted in rapid neonatal death due to disruption of the skin barrier formation [76]. To circumvent this lethal skin phenotype, Enquist et al. generated the conditional Mx1-Cre+ Gba1flox/null knockout model, which was capable of proper fetal skin development [67]. Using the Mx1/Cre-loxP system, Cre-mediated deletion of Gba1 exons 9–11 was postnatally induced through the administration of polyinosinic-polycytidylic acid, which activates the Mx1 promoter. GCase activity was abolished in the spleen and significantly reduced in the liver and bone marrow following exon excision. The induced Gba1 knockout mice exhibited high levels of GluCer, splenomegaly, and microcytic anemia, and Gaucher cells were observed in hematopoietic tissue. No CNS involvement was detected due to the limited activity of the Mx1 promoter in the brain and the lifespan was normal, rendering the model most analogous to symptomatic type 1 GD [67,68]. The generation of models of the neuronopathic forms of GD has been challenging [77]. A K14-lnl knockout mouse line was developed by the Karlsson group in an effort to address the challenges previously associated with the development of an nGD murine model [78]. The loxP-neomycin disruption of Gba1 in these mice was coupled with Cre-recombinase regulated by the keratinocyte-specific K14 promoter. This model enabled Gba1 expression in the skin, which prevented neonatal death. At roughly 10 days of age, the mice rapidly deteriorated. They developed motor dysfunction and seizures, and neuropathologic evaluations revealed neuronal loss, microgliosis, and astrogliosis. K14-lnl mice have markedly reduced GCase activity and abnormal levels of GluCer in the brain, liver, and spleens, as well as the presence of Gaucher cells in visceral tissues. They typically succumbed within the first 2 weeks of life, thus providing a relevant, albeit short-lived, model that is representative of severe type 2 GD. To elucidate the role of GCase-deficient microglia in the neuropathology of type 2 GD, Enquist et al. crossed their Gba1flox/flox mice with Nestin-Cre mice to generate the Nestin-flox/flox mouse [67,78]. In this model, Gba1 was knocked out exclusively in neuronal and neuroglial cell precursors without disturbing GCase in the microglia. Nestin-flox/flox mice developed similar symptoms to the K14-lnl mice, including abnormal gait, limb rigidity, and end-stage paralysis. However, symptom onset and progression were delayed in comparison to the K14-lnl model. Du et al. used the Gba1flox/flox mouse model to create another nGD model alongside the Nestin-flox/flox mouse [69,78]. They crossbred Gba1flox/flox with UBC-CreERT2 mice and Nestin-Cre mice to generate the Gba1flox/flox, UBC-CreERT2 and Gba1flox/flox, Nestin-Cre genotypes, respectively. Similar to the Mx1-Cre+ Gba1flox/null mice, Gba1flox/flox;UBC-CreERT2 is a conditional Gba1 knockout model. In this model, Cre recombinase, bound to a mutant estrogen receptor (T2), is activated only after exposure to the chemical tamoxifen. This activation, driven by the UBC promoter, subsequently deletes Gba1 throughout the entire body. After repeated intraperitoneal tamoxifen injections, the Gba11flox/flox;UBC-CreERT2 mice rapidly display weight loss, motor dysfunction (including abnormal gait and hyperextension of the neck), and seizures, and died within 7 days after induction. Gaucher cells were observed in the brain, liver, and spleen, and GCase activity was significantly reduced in the brain, liver, and spleen [69]. The Gba1flox/flox, UBC-CreERT2 mouse provides a viable model that mimics the systemic and CNS involvement observed in nGD, and the conditional nature of the model allows flexibility to study the effects of therapy in mice at different ages. 2.3. Gene Delivery Vectors and Outcomes Glucocerebrosidase is only secreted when cells express high levels of the enzyme. Thus, constructed vectors must be able to promote production of GCase very efficiently in order to have a therapeutic benefit while maintaining a favorable safety profile [62]. To achieve such an outcome, various combinations of viral vectors, serotypes, and promoters have been tested to deliver human GBA1 (huGBA). 2.3.1. Non-AAV Gene Delivery Vector Several non-AAV vectors have been considered for gene therapy for GD, including the adenovirus [62], retroviruses [67,79], and lentiviruses [68]. Marshall et al. created a recombinant adenovirus vector by replacing the E1 region of adenovirus serotype 2 (Ad2) with the human cytomegalovirus (CMV) immediate early promoter and enhancer [62]. A high dose of this vector in wild-type mice was able to increase GCase expression by 100 fold in the liver and 10 fold in the spleen and lungs as well as promoting secretion of GCase into serum. Testing their construct in CBE-induced murine models showed that both intravenous and intranasal delivery could produce Kupffer-targeted GCase that could reduce the accumulated GluCer in the liver. A low dose of the vector was also able to clear GluCer levels from Kupffer cells despite producing levels of GCase that were not detected in serum, likely due to the enhanced ability of adenoviruses to directly transduce Kupffer cells [62]. However, adenoviruses tend to be highly immunogenic, and the uptake of adenoviruses by Kupffer cells via the innate immune response paradoxically reduces the efficacy and longevity of the viral vector [80,81]. Enquist et al. used a retroviral vector with the spleen focus-forming virus (SFFV) enhancer-promoter to induce GCase expression in hematopoietic stem cells that were then transplanted into GD mice. This vector was capable of elevating GCase enzyme activity in the bone marrow, spleen, and liver and subsequently normalized substrate levels despite relatively low gene marking. Gaucher cells were almost fully eliminated in the treated model, whereas untreated mice continued to develop and exhibit the GD phenotype [67]. However, retroviruses possess the risk of genotoxicity, particularly when combined with a strong long terminal repeat enhancer-promoter such as SFFV and thus may not have a suitable safety profile for clinical gene therapy [82,83]. Lentiviruses such as HIV-1 possess a narrow tropism for nondividing cells such as primary T lymphocytes, CD34+ cells, dendritic cells, and macrophages, allowing for improved delivery to the desired gene therapy targets for GD [84]. Lentiviruses also demonstrate greater safety and less risk of insertional proto-oncogene activation than gammaretroviruses [85].Kim et al. evaluated the viability of an HIV-1-based lentiviral vector driven by the human elongation factor 1-α (EF-1α), which is a versatile and relatively potent promoter, particularly in hematopoietic stem cells [65,86]. EF-1α has improved stability, transgene expression, and transfection efficiency over traditional viral promoters such as CMV [87]. In C57BL6/J mice, this vector distributed widely into various cells and produced supraphysiological levels of GCase activity within various visceral tissues eight weeks after portal vein or tail vein injection. This elevated expression was consistently sustained in these tissues over the four months of the study, although no transduction was observed in the brains of the treated mice. Mice injected via portal vein exhibited greater GCase activity than mice injected via tail vein but developed mild hepatic toxicity post-injection. Despite the demonstrated efficacy of the HIV-1-based lentivirus, the source of the vector carries the concern that the parent virus could reconstitute into a replication competent virus [88]. To ease this concern and further reduce their oncogenic risk, self-inactivating (SIN) lentiviral vectors have been developed by removing the transcriptional elements of HIV-1 [89,90]. Dahl et al. transduced bone marrow cells with SIN lentiviral vectors and transplanted them into pre-symptomatic and symptomatic Mx1-Cre+ Gba1flox/null mice. They compared the safety and efficacy of two SIN lentiviral vectors containing the human phosphoglycerate kinase (PGK) and CD68 promoters, respectively, against an SIN lentiviral vector with the SFFV promoter [68]. PGK is a relatively weak promoter that produces physiological rather than supraphysiological gene expression and is expressed ubiquitously, whereas CD68 is a macrophage-specific promoter [91,92]. Both vectors successfully reversed splenomegaly, elevated GCase activity, and prevented GluCer accumulation in the bone marrow, spleen, and liver when administered pre-symptomatically. In mice that had already developed symptoms, both vectors also significantly increased GCase activity. However, in contrast to the SFFV-positive control vector, which increased activity levels to 9.5 fold of wild-type levels, neither the PGK nor CD68 SIN lentiviral vectors restored GCase activity to wild-type levels. Nonetheless, the resulting activity levels were sufficient to reduce GluCer accumulation and dramatically reduce the number of Gaucher cells. Mice treated with either vector also exhibited near-normal spleen size as well as improvement in several blood parameters. All vectors displayed sustained expression up to at least 20 weeks. The SFFV promoter produced the highest levels of GBA1 expression across all evaluated tissue types and cellular subsets, including progenitor cells. The CD68 and PGK promoters both expressed the transgene in tissue, lymphoid compartments, and granulocytes, but the CD68 promoter resulted in higher transgene expression in monocytes and macrophages. Thus, although the PGK and CD68 promoters produced less robust results than the SFFV promoter, they were still capable of preventing and reversing the GD1 phenotype without the safety risks associated with a stronger promoter like SFFV. 2.3.2. AAV Gene Delivery Vectors Adeno-associated viruses have been the primary viral vector used for in vivo gene therapy of GD given their relative safety compared to adenoviruses and lentiviruses, ability to sustain production of the transgene product, and ability to deliver the product to both dividing and nondividing cells. Although there are dozens of AAV serotypes, only a select few have been examined as vectors for GD, as they appear to have the most relevant tropisms. The AAV2 serotype has been widely evaluated in gene therapy, and most recombinant AAVs contain the AAV2 ITR sequence [93]. This serotype exhibits preferential tropism for smooth muscle, skeletal muscle, CNS, liver, and kidney [94]. Hong et al. combined an AAV2 vector with the EF-1α promoter and delivered it via the portal or tail vein to determine its therapeutic feasibility for GD [64]. Although vector distribution, GCase expression, and GCase activity varied among tissue types, time points, and delivery methods, all treated mice exhibited significantly increased levels of GCase activity in the liver, spleen, and lung within two to six weeks after injection. However, activity began to decrease by 20 weeks after injection, with GCase activity in the lung dropping to baseline levels. Treated mice did not exhibit signs of toxicity or abnormal behavior, presenting a promising safety profile for this recombinant AAV2 vector. Despite its established efficacy, the longevity of the vector was not established, and Hong et al. posited that the AAV8 serotype would be a more optimal option for GD due to its stronger expression in liver [64]. Subsequently, Marshall et al. compared the efficacy of the AAV2 serotype to the AAV2/8 pseudotype [63]. The AAV2/8 pseudotype is a chimeric packaging plasmid in which the AAV2 capsid is removed and the AAV2 gene is fused with an AAV8 capsid. This pseudotype was designed to take advantage of the well-characterized longevity of the AAV2 serotype, as well as the immunological distinctiveness and greater liver tropism of AAV8 [95]. Marshall et al. constructed their vectors with the DC172 promoter, which produced a significantly higher GCase hepatic-restricted transgene expression than the CMV or DC190 promoters. This tissue-restricted promoter reduced the risk of off-target effects and an undesired host immune response. Both vectors produced supraphysiological levels of GCase that was secreted into the systemic circulation and normalized GluCer levels in treated mice following intravenous injection. However, the AAV2/8 vector was 50 to 100 fold more efficacious than the AAV2 vector, indicating that the AAV8 serotype is indeed more suitable for GD [63]. The same group then tested a pseudotyped AAV8 vector combined with the DC172 promoter administered intravenously in pre-symptomatic and symptomatic mice. In the pre-symptomatic mice, McEachern et al. reported supraphysiologic levels of GCase in the serum and liver and 50% of normal levels in the spleen and lungs. These findings were accompanied by normal GluCer levels and the absence of Gaucher cells, indicating that the vector was able to prevent GD pathology from developing. In older symptomatic mice, supraphysiologic levels of GCase were also attained, albeit in a dose-dependent manner. Even the lowest tested dose was sufficient to clear GluCer accumulation and storage. For both groups, the improved GCase levels were sustained for at least six months, demonstrating the long-term efficacy of the vector [66]. To measure the effectiveness of gene therapy for nGD, Massaro et al. developed an AAV9 vector with a human β-glucuronidase (GUSB) promoter [47]. AAV9 has been shown to cross the BBB and produce widespread expression in neurons as well as liver, heart, and skeletal muscle [96]. The nGD mice that were injected in utero did not develop behavioral symptoms, neuroinflammation, neuronal loss, or evidence of storage for up to 35 days. Longer-term analysis indicated that mice treated in utero appeared normal and fertile at day 70. However, by day 100, these mice performed worse on motor tasks, weighed less than wild-type littermates, and exhibited higher than normal microglial activation and astrogliosis. GCase activity and GluCer levels were similar to wild-type, although higher levels of other glycosphingolipids were detected. Thus, this AAV9 vector was effective in preventing neonatal death and delaying onset of symptoms but appeared to lose potency later in development. Massaro et al. also examined the utility of their vector when administered intravenously or intracerebroventricularly in newborns. No behavioral changes or weight loss was observed in treated nGD mice for up to at least 180 days, regardless of delivery method. Supraphysiological and physiological levels of GCase were observed in various brain regions. Evidence of neuronal loss and cortical thinning was observed in several brain regions of mice treated via IV infusion. In visceral organs, both delivery methods significantly increased GCase levels, with the IV route preventing splenomegaly and development of Gaucher cells. However, intracerebroventricular administration did not ameliorate visceral pathology despite the increased GCase. Therefore, while the AAV9 vector was able to prevent neonatal lethality in all cases, it was most effective against both neurological and visceral symptoms when delivered postnatally via IV injection [50]. Du et al. tested an AAV9 vector expressing mouse Gba1 driven by a CMV promoter in tamoxifen-induced GD mice. The group administered the construct 15 and 30 days before tamoxifen induction to achieve peak expression prior to symptom onset as the decline following tamoxifen injection is too rapid for the vector to reach efficacious expression levels. Administration of the vector 15 days prior to tamoxifen induction did not demonstrate a therapeutic benefit, only prolonging survival by one to two days. However, intravenous vector administration 30 days prior to tamoxifen induction substantially extended lifespan to 14 times longer than untreated mice and greatly improved motor behavior. GCase activity was significantly increased in brain, liver, and spleen, and no toxic effects were detected even at the highest dose. However, the delay in transduction led the group to conclude that this vector is not a feasible approach for GD2 [69]. Du et al. also developed an AAV9 vector targeted specifically for nGD by driving Gba1 expression with a neuron-specific Synapsin 1 (hSyn1) promoter in mice whose Gba1 gene was only deleted in neural and glial cells. The vector was administered intraperitoneally prior to symptom onset, enabling normal weight gain and doubling the lifespan of the treated mice. GCase activity was significantly elevated in the cortex of treated nGD mice compared to untreated, although liver and lung were unaffected. Neuronal loss, astrogliosis, and microglial activation were also reduced, but not fully ameliorated. Thus, the AAV9-hSyn1 vector is capable of lessening, but not preventing, brain involvement without impacting the viscera. Furthermore, only the highest dose that was tested was efficacious, indicating that the AAV9-hSyn1 vector requires relatively higher doses, which may reduce the safety profile of this construct [69]. Massaro et al. also tested a single-stranded AAV9-hSyn1 vector containing a woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) to express human GBA1. In brain, the vector was neuron-specific, and expression was also detected in several visceral organs, as well. The vector was administered to an nGD mouse model on the day of birth, prolonging lifespan and enabling normal weight gain without evidence of neurotoxicity. Compared to wild-type controls, treated mice exhibited similar motor behavior, glycosphingolipid levels, and levels of neuroinflammatory markers in the brain at 60 and 66 days of age. GCase activity in the brain of treated mice was around 68% of wild-type, but this difference was not significant. Unlike their AAV9-GUSB construct, Massaro et al.’s AAV9-hSyn1 vector fully prevented neuronal loss and preserved cortical thickness. The AAV9-hSyn1 vector also improved visceral pathology, preventing splenomegaly and Gaucher cell accumulation in liver, spleen, and heart. Thus, this construct showed promise for treating both neuronopathic forms of GD [70]. Several factors may have contributed to discrepant findings in the studies by Massaro et al. compared to Du et al. For example, Massaro et al. tested an 8-fold higher dose and injected their mice at a younger age [70]. Additionally, WPRE has been demonstrated to enhance transgene expression in single-stranded AAV vectors, which likely also contributed to the greater efficacy observed compared to the vector constructed by Du et al. [97]. 3. Current Clinical Trials Currently, there are a few active gene therapy clinical trials for the treatment of GD. The first (GALILEO-1), “A Gene Therapy Study in Patients with Gaucher Disease Type 1” (NCT05324943), conducted by Freeline Therapeutics, involves the administration of a liver-directed ssAAV to participants as a one-time intravenous infusion. The group made 37 GBA1 AAV constructs, which, when infused in mice with RC-04-26, resulted in the robust uptake of GCase by cells in spleen, bone marrow, and lung [98]. At this time, no results have been reported from the patient trial. Another active clinical trial, “Phase 1/2 Clinical Trial of PR001 in Infants With Type 2 Gaucher Disease (PROVIDE)” (NCT04411654), is being conducted by Prevail Therapeutics and Eli Lilly & Company. This trial involves the injection of LY3884961, an AAV9 construct encoding wild-type GBA1, intracisternally in type 2 infants pretreated with methylprednisolone and sirolimus. Oral prednisone is taken concomitantly. The study aims to evaluate the immunogenicity of AAV9 and measures GCase in the blood and cerebrospinal fluid. No results have been shared at this time. The same companies have also initiated a phase 1/2 study in GD1, AVR-RD-02, compared to enzyme replacement therapy, for the treatment of GD1 (NCT04145037 PROCEED), with intravenous administration of their construct. Studies designed to evaluate the efficacy and safety of autologous hematopoietic stem cell (HSC) gene therapy using a lentiviral vector for GD1 and GD3 (NCT05815004) by Avrobio were recently withdrawn voluntarily and not due to safety or medical reasons. However, outcome measures from the few patients who completed the 52-week clinical trial indicated low vector copy numbers per cell, slight reduction in spleen and liver size, slight reduction in glucosylsphingosine levels, no changes in hemoglobin or platelet levels, and minimal increase in GCase enzyme activity that decreased over time. 4. Future Directions for Gene Therapy for Gaucher Disease The development of gene therapy for GD has focused on adeno-associated viral vectors because of their relatively low risk of immunogenicity and stable expression of the gene target. While the stable expression of target genes in the nervous system is the most important factor for the development of AAVs to treat nGD, it is also desirable to express GBA1 systemically to treat pathology in visceral organs. Since the combination of an AAV9 serotype vector with a constitutive promoter (such as GUSB) fulfills the criteria for neurological and visceral expression, this combination has been widely used in clinical trials of gene therapy to treat neurological disorders [99] and other LSDs [100] and in pre-clinical trials for GD [50,70]. Conversely, the ubiquitous expression of AAV9 may result in undesired off-target toxic side effects [101]. To overcome this limitation, other serotypes such as AAVrh10 have been developed. These serotypes have been shown to enhance transgene expression in the central nervous system with lower immunogenic side effects when compared to AAV9 [102]. However, further testing is required to analyze their efficacy for treating nGD. Most AAVs used in pre-clinical trials are designed using single-stranded DNA (ssAAV) genomes. The time to peak expression for these vectors is limited, as they must first be converted to double-stranded DNA to begin gene expression, which may present challenges for successfully treating forms of GD that develop symptoms perinatally [103]. The conversion of ssAAVs to their double-stranded counterparts may also reduce the efficacy of the vector. An alternate AAV construct that has been proposed uses a self-complementary vector (scAAV), which contains an inverted dimeric repeat genome that folds into dsDNA without the aid of DNA synthesis molecules. These vectors have been notably effective at transducing multiple tissue types, including nervous tissue, and circumventing the limitations associated with the conversion of ssAAVs. Vector construct size in scAAVs must be reduced to approximately 2500 base pairs to prevent the dimeric repeats from exceeding the size limitations of the normal AAV packaging capacity (approximately 4700 nucleotides); the two halves of the scAAV are thus complementary. The transduction efficiency of scAAVs should be considered when designing vectors for future gene therapy studies in GD [103]. When developing an efficacious construct, consideration must also be given to the route of administration and timing of delivery of the vector. Intracerebroventricular injection may be the most reliable method to cross the BBB, but the procedure is risky and invasive and may lead to uneven distribution of the vector. Systemic injection is therefore safer and more predictable, but these routes typically produce lower vector expression and gene marking, which may compromise effectiveness [104]. To ensure successful clinical studies of gene therapy, more rigorous pre-clinical trials must be designed to further establish the efficacy and safety of different adeno-associated viral vectors, as well as variations in those vectors (including scAAVs and AAVrh10). Additionally, longitudinal studies are necessary to establish the longevity of adequate GBA1 expression. This might indicate the need for additional vector injections periodically or the need to supplement other treatment modalities such as SRT or ERT. Although AAVs do not cause significant infection without the aid of a secondary viral host, they could still trigger an unpredictable immune response for a variety of reasons. Antibodies to previous infection by AAVs or adenoviruses may conceivably diminish the response to the therapy or prevent a response altogether and could be dangerous to the patient [105]. A prior adenoviral infection with a similar serotype of adenovirus may result in a strong immune response post-treatment. This could give rise to serious complications including meningitis, encephalitis, and, in rare cases, death. The immunogenicity can also be impacted by insertional mutagenesis, which can preclude genotoxicity [106]. There are alarming reports in both mammalian models and human subjects of the genotoxicity resulting in hepatocellular carcinoma (HCC) [107], despite most cases in humans being episomal and benign. Thus, it is crucial to consider vector design with respect to possible undesirable integrations into the host genome to avoid carcinogenic outcomes [101]. One side effect that has been observed in clinical trials of AAV gene therapy in other neurological diseases is thrombotic microangiopathy, which is associated with an immune activation that gives rise to vascular pathologies and may result in ischemia of the brain and other organs [99]. This may be overcome by consideration of alternate administration routes of AAV such as intra-CSF infusions, which could reduce the availability of circulating AAV [99]. Treating GD2 is particularly challenging, as the window between time of diagnosis and irreversible neurological damage may be very small. However, newborn screening campaigns have allowed for identification of cases prior to symptom development, which may be integral to administering treatment early enough to drastically alter the disease course. It still remains possible, however, that irreversible CNS damage in GD2 has already begun prenatally, as elevated glucosylsphingosine levels have been documented during early gestation [108]. Nevertheless, we remain cautiously optimistic that viral gene therapy can be used to ameliorate the symptoms in at least some forms of neuronopathic GD. These therapies should be examined thoroughly and developed carefully to improve the outcomes for individuals with nGD. There are some ethical concerns that persist regarding the use of gene therapy in young patients. There is still inadequate clinical data to conclude that these gene therapy modalities will completely reverse—or cure—disease progression and manifestations. As such, they may only partly treat a patient’s disease at a potentially very high cost [100]. Partial therapy in GD2 may prolong, but not prevent, the neurodegenerative course. Furthermore, patients may need to continue to receive additional costly therapies. The risk of minimal improvements to a patient’s quality of life is thus important to consider and to further examine through ongoing pre-clinical and clinical trials. However, there are indications of promising results of viral gene therapy in other LSDs [100]. We thus believe that the further development and evaluation of improved gene therapy vectors, modes of administration, and construct optimization can ultimately be of significant benefit to patients with all forms of GD. |
doc2 | Background Gaucher’s disease (GD), a rare condition, represents the most common lysosomal storage disorder. The cardinal manifestations of GD are fatigue, hepatosplenomegaly, anemia, thrombocytopenia, bone pain, and bone infarction, thereby culminating in a marked deterioration of patients’ quality of life (QoL). Patient-reported outcomes (PROs) offer valuable insights into the impact of GD on patients’ QoL and symptoms. This systematic review aimed to identify and analyze PROs and outcome measures in GD patients. Methods We systematically searched PubMed, Web of Science Core Collections, EMBASE, SCOPUS, Cochrane Library, PsycINFO, Wan Fang Data, China National Knowledge Infrastructure (CNKI), and the Chinese Biomedical Literature Database (CBM). The methodological quality of the included studies was assessed using a mixed methods assessment tool. Results A total of 33 studies were identified, encompassing 24 distinct patient-reported outcome instruments, with the most frequently employed instrument being the SF-36. The study designs included eighteen cross-sectional studies, seven pre- and post-intervention investigations, three randomized controlled trials, two cohort studies, two qualitative inquiries, and one validation study. These studies explored diverse domains such as the QoL and cardinal symptoms (e.g., fatigue, pain, bleeding, cognition, social relationships, and psychological functioning) in patients with GD. Furthermore, significant attention was directed towards the appraisal of the therapeutic benefits of various interventions in patients with GD. A novel GD-specific instrument has also been developed, which has two applied versions: a 24-item variant for routine clinical monitoring and a 17-item form for use in clinical trials. Conclusion PROs have garnered increased attention and concern in the realm of GD. Despite this progress, it is noteworthy that the instruments used to measure PROs in GD are still predominantly generic instruments. While researchers have endeavored to develop and validate a disease-specific instrument, currently the use of this instrument is limited. Owing to several challenges, including the small number of patients, heterogeneity of the disease, and cross-regional discrepancies in study findings, GD poses substantial difficulties in the measurement of QoL and development of instruments. Consequently, patients with GD require more dependable measurement instruments that accurately reflect their QoL, efficacy of treatment, and facilitate healthcare decision-making. Background Gaucher disease (GD) is a rare autosomal recessive genetic disorder caused by a pathogenic variation in the GBA1 gene [1]. GD is the most common lysosomal storage disorder with an estimated incidence of around 1 in 40,000–60,000 individuals in the general population [2, 3]. The GD phenotype is heterogeneous and clinically divided into three subtypes (1, 2, and 3), with GD-1 accounting for the majority of cases at approximately 90–95% [4]. GD-1, also known as non-neuropathic GD, is distinct from types 2 and 3, referred to as neuropathic GD [5]. The most common symptoms of GD include fatigue, hepatosplenomegaly, anemia, reduced platelet count (leading to easy bruising and prolonged clotting time), bone pain, and bone infarctions that often damage the shoulder or hip joints [5]. These symptoms have a profound impact on patients’ quality of life (QoL) in areas such as impairment of daily activities, self-care, body image, relationships with family, work performance, or school [6, 7]. At present, the primary clinical approaches for GD management are substrate-reduction therapy (SRT) and enzyme replacement therapy (ERT) [8]. Although both ERT and SRT are efficacious treatments, they are invasive, costly, and require patients to modify their work and personal schedules [6]. Patient-reported outcomes (PROs) have been defined as any information “of a patient’s health condition that comes directly from the patient, without interpretation of the patient’s response by a clinician or anyone else” [9]. PROs have gained increasing prominence in the health technology assessment process, following the rise of a patient-centered approach to healthcare [10]. PROs data can provide valuable evidence to facilitate shared decision making, labeling statements, clinical guidelines, and health policy [11]. Owing to the special characteristics of rare diseases, such as high unmet need, severity and debilitating nature of the condition, and a dearth of appropriate data, there is a heightened necessity to supplement traditional measurement methods with PROs in a creative and pragmatic manner [12]. The principal methods employed for gathering PROs include qualitative interviews and patient-reported outcome measures (PROMs), with the latter being the primary measurement instrument. PROMs are validated questionnaires that possess robust psychometric properties and are commonly implemented in clinical trials and disease management [9]. In summary, utilizing PROs to comprehend the health status and treatment outcomes of GD patients is a critical step towards enhancing patient care and healthcare decision-making. Numerous studies have investigated patients with GD using PROMs or qualitative methods. Self-reported symptoms [13] of GD patients (e.g., fatigue, pain, bleeding swelling, and anemia) have a serious impact on patients’ QoL [14, 15], mental health [6, 16], social functioning [17], and cognitive abilities [18]. Some studies have also illustrated the effects of ERT and other interventions on patients’ QoL [19, 20]. In addition, a disease-specific instrument for GD was developed and validated [21]. However, comprehensive reviews of the use of PROs and core outcomes in GD patients have been limited. Therefore, we conducted a mixed-methods systematic review to conceptualize the stipulated overall understanding of QoL in GD and identify challenges to greater implementation and interpretation that can benefit from further research. Methods This review was conducted in accordance with the PRISMA guidelines [22]. The review protocol was registered with PROSPERO (https://www.crd.york.ac.uk/prospero/; Registration ID: CRD42020192027). Search strategy English and Chinese databases were included to consider the linguistic expertise of the review authors. We systematically searched the following databases: PubMed, Web of Science Core Collections, EMBASE, SCOPUS, Cochrane Library, Wan Fang Data, China National Knowledge Infrastructure, and Chinese Biomedical Literature Database. All dissertations from the inception of each database until January 2023 were considered. Two groups of search terms (Additional file 1) were used:1) PRO related terms and 2) GD-related terms. Moreover, the references were manually searched for additional papers. As our search did not include many clinical trials, it was expanded to include other study designs (e.g., pre-post studies, cross-sectional studies, and qualitative studies). Selection and data extraction Studies were independently screened by two reviewers (JCF or YW), based on whether their title and abstract adhered to the selection criteria (GD, English or Chinese studies, and related to PROs or QoL) to determine their eligibility for inclusion in the full-text review. Studies were excluded for the following reasons: non-GD disease, not in English or Chinese, case study design, out-of-scope population (e.g., non-human subjects), and secondary paper. The publication years were not limited. Subsequently, the full texts of potentially eligible studies were searched and independently screened by the two reviewers. After each reviewer completed the two processes, any differences were resolved through discussion or consultation with a third investigator (SPL). The two independent reviewers then extracted the following data from each study: study design, patient characteristics, treatments, PROMs, and primary outcomes. Methodological quality appraisal The methodological quality of the included studies was independently assessed by two review authors (JCF and YW) using the Mixed Methods Assessment Tool (MMAT) [23]. MMAT is a unique tool that allows the reviewers to assess the methodological quality of studies of different designs (qualitative, quantitative and mixed methods studies) in systematic mixed research reviews [24]. The MMAT guidelines discourage the calculation of an overall score from the scores for each criterion and recommend a more detailed presentation of the scores for each criterion to better understand the quality of the included studies. The exclusion of studies with low methodological quality is usually discouraged. Because there are only a few criteria per domain, a descriptor, such as a star (*) or a percentage, can be used to indicate the score. Results Results from the literature searches A total of 7360 studies (including 93 Chinese articles) were identified, with 4674 remaining after the removal of duplicates, and 85 remaining after the review of titles and abstracts. Of these, 85 met the full-text review criteria, and 33 met the inclusion criteria. Figure 1 summarizes the flow of the articles through the selection process. Fig. 1 figure 1 PRISMA flowchart describing the identification, selection and inclusion of studies on PRO in Gaucher’s disease Full size image As shown in Fig. 2, there was a clear trend toward an increase in the number of published studies with PROs endpoints over time, especially since 2016. The studies were conducted mainly in high-income countries, with the top three being the United States, Spain, and Israel; the number of studies in China was equal to that in Israel because of the inclusion of relevant studies in Chinese. PROMs measuring the overall QoL were used more frequently than symptom-directed instruments, and the most commonly used instrument was the Medical Outcomes Study Health Survey Short Form-36 Item (SF-36), which was employed in 17 studies. Fig. 2 figure 2 Number of GD publications per year involving PROs Full size image The general characteristics of the included studies are summarized in Table 1. Of the thirty-three included studies, eighteen were cross-sectional, seven were pre- and post-intervention investigations, three were randomized controlled trials (RCT), two were cohort studies, two were qualitative studies, and one was a validation study. The following is a summary of the results of the literature review of the different biomedical literature databases. It is organized by the study design into clinical trials, longitudinal observational studies, cross-sectional studies, and pre- and post-intervention investigations. Table 1 Characteristics of included studies Full size table Methodological quality of the included studies The overall quality score was 100% (5 of 5 criteria met) for seventeen studies (51.5%), 80% for seven (21.2%), 60% for seven (21.2%), 40% for two (6.1%), and 20% for zero (0%) studies, as shown in Table 1. The most common causes for downgrading the quality assessment were small sample size, lack of inclusion and exclusion criteria, measures not validated, and reliability tested. Considering the small number of patients with rare diseases, studies that included more than 15 patients were considered to meet the sample size requirement; however, six studies did not meet this requirement. Among clinical trials, open-label trials were the most common. Clinical trials Three clinical trial studies were reviewed, including two pharmaceutical clinical trials (miglustat and eliglustat) [25, 26] and one evaluating the effects of iron chelation therapy [27]. All clinical trials used the SF-36 as a clinical outcome assessment measure, and one trial applied the Fatigue Severity Scale. In a 24-month, randomized, open-label phase II study, 36 patients with GD-1 of varying clinical severity were enrolled in the study to examine the safety and efficacy of oral miglustat [25]. The 24-month period included a 6-month randomized trial and an 18-month extension period. A total of thirty-six patients were randomly assigned to three intervention groups (miglustat alone, imiglucerase + miglustat, and imiglucerase alone) and their QoL was assessed using the SF-36. At 6-month, there was a significant difference in the mean changes from baseline in SF-36 Mental Health between patients receiving miglustat (who improved) and those receiving imiglucerase or combination therapy (who deteriorated). Additionally, the miglustat group reported greater convenience and satisfaction with the treatment. Another study reported the final 8-year outcomes of previously untreated 19 adults with GD-1 who completed an open-label phase II trial of eliglustat. The administered QoL measures included the SF-36 and Fatigue Severity Scores [26]. The mean QoL and disease severity improved significantly during the first 3–4 years of eliglustat treatment, with only slight changes in the values during the remainder of the study period. Among the 16 patients with baseline and 8-year values, the mean (± standard deviation [SD]) of Fatigue Severity Score (1 = least severe, 7 = most severe) had decreased by 24% from 4.44 ± 1.79 to 3.28 ± 1.62 at 8 years. The last open-label RCT analyzed the data of eight patients with GD, and the QoL was measured by the SF-36 after the patients received two iron chelation therapies (deferasirox or deferoxamine). At 4 weeks and 4 months, there was no significant difference between the two iron chelation therapies in terms of the patients’ QoL physical component scores [27]. Cohort studies The present review includes two longitudinal studies, a retrospective study [28] and prospective [29]. The 12 months retrospective cohort study was conducted to investigate the differences in the clinical and subjective well-being of 34 GD-1 patients experiencing ERT dosage reduction after a forced temporary imiglucerase shortage. The results showed that drug reduction did not induce a substantial modification in the laboratory values but seemed to have influenced the perception of well-being of some GD patients [28]. The prospective cohort study included 48 patients with GD who underwent total hip replacement. QoL, hip function, and pain were assessed using the EQ-5D, hip-related disability (HHS) score, and visual analog scale (VAS), respectively. Strong linear correlations were found among the indices themselves, that is, between HHS and VAS (R = 0.505), HHS and EQ-5D (R = 0.88), and EQ-5D and VAS (R = 0.614) [29]. Cross-sectional studies and qualitative research We included eighteen cross-sectional studies and two qualitative studies. These studies focused on evaluating the QoL of patients with GD and analyzing the influencing factors associated with the patients’ QoL, both positive and negative. GD severely affects several major QoL dimensions [7, 13, 19, 20, 30,31,32,33,34,35]. Patients with GD scored significantly worse than did the age- and sex-adjusted normal population on five of the eight SF-36 subscales (p < 0.05) [20]. The median health status score on the EQ-5D for patients with GD in the UK was 0.727 (confidence interval [CI], 0.691–0.796), with three patients having a health status score < 0 [30]. The results showed that physical symptoms, such as bone pain, chronic fatigue, bleeding, and splenomegaly, can cause patients to exhibit moderate to severe psychological complications (e.g., anxiety, depression, and feelings of isolation) that interfere with daily life, school, work, and social activities [13]. Moreover, qualitative studies have found that experience a variety of stresses, and that discomfort, inconvenience, and the high cost of treatment can also cause psychological problems for patients [6, 13]. A study found that although children’s and parents’ PedsQL 4.0 scores were consistent (i.e., the coefficients for internal consistency exceeded 0.70 for the majority of the subscales in both self-report and parent proxy-report versions), the pattern of association between symptoms and perceived burden was different for children and parents [7]. In children, the presence of symptoms such as bone, joint, or abdominal pain had a significant impact on the reported QoL; however, the QoL was more significantly affected by frequent or abnormal bleeding and fatigue in children in parent proxy reports [7]. Several cross-sectional studies have identified factors associated with the QoL of patients with GD [6, 7, 13, 20, 30, 32, 34,35,36,37]. ERT treatment is the most important factor for improving the QoL of patients, and the earlier it is received, the more significant the effect [35]. Bone, joint, or abdominal pain; bleeding; joint replacement; spleen replacement; and fatigue have a negative impact on the QoL [7, 13, 20, 36]. In clinical practice, it is necessary to distinguish between bone pain and neuropathic pain in patients with GD in order to consider the most appropriate disease management and facilitate patient care and prognosis [38]. A study in Bulgaria reported a statistical correlation between the cost of medication and QoL [31]. The high incidence of neurological symptoms in patients may be related to concurrent medical problems and/or the side effects of concurrent medications [39]. Parkinsonism and other neurological symptoms may be a significant burden for patients with GD; however, symptomatic management can improve their QoL [40]. Type 2 and 3 GD are often associated with neurological involvement and symptoms such as dysphagia, dyspnea, epilepsy, Parkinson’s disease, and cognitive decline. Cognitive impairment and depression may be early predictive factors for Parkinsonism in the GD population [36]. The vitality and neurological symptoms in patients with GD are also significantly affected, and daytime sleepiness is a common symptom [40]. Pre- and post-intervention investigations Seven studies evaluated changes in the QoL before and after ERT/SRT treatment [14, 15, 41,42,43,44,45], and one study also considered acupuncture [45]. The SF-36 was the most commonly used instrument, while the Lansky Play-Performance Scale was used to assess treatment the outcomes in children. After ERT/SRT treatment, patients with GD experienced a reduction in bleeding, chronic fatigue, gastrointestinal discomfort, and bone pain, and a significant improvement in psychosocial functioning [15, 41, 42, 44]. The SF-36 showed an improvement in vitality (energy level and fatigue) first [15]. Bone pain was relieved after treatment but remained an important influencing factor for the QoL [14, 44], and the psychological status did not improve significantly after the intervention [15]. The use of ERT every two weeks showed substantial benefits and significantly improved the QoL, assessed with the Lansky Score, in five children with GD-1 [43]. Acupuncture, an ancient Chinese therapy, has been used to treat patients with GD. A total of 12 patients participated in the treatment, and while the only pain outcome reduced by acupuncture was knee pain, significant improvements were observed in almost all FACIT fatigue measures [45]. Validation and introduction of a disease-specific scale GD-specific scales have been developed, including two applicational versions: a 24-item version for routine clinical monitoring (rmGD1-PROM) and a 17-item version for clinical trials (ctGD1-PROM), with psychometric properties measured using the ctGD1-PROM [21]. The instrument was developed in three countries (US, France, and Israel) and resulted in three versions in: Hebrew, Arabic, and English. The rmGD1 PROM was used in a cross-sectional survey in 2020 [46]. The use of a GD-1 specific PROM highlights personal problems that are not captured by traditional outcome parameters (i.e., GD1-related restrictions and concerns, fatigue, physical weakness, bone pain, and worry regarding the future) [46]. The psychometric results showed strong evidence of convergent validity based on correlations between the overall and item-level ctGD1-PROM scores and summary scores of the physical and mental components of the SF-36 [21]. In addition, the internal consistency of the ctGD1-PROM was excellent (Cronbach’s alpha = 0.928) [21]. Discussion Our review analyzed 33 studies pertaining to patients with GD, which incorporated patient-reported outcomes and were published after 1993. Notably, the number of publications per annum has demonstrated a consistent and upward trajectory, rising from a mean of 0–1 publication yearly to 3–5 publications annually in recent times. Indeed, this tendency is related to the importance given to QoL by official health technology assessment bodies, and for rare diseases, the role of QoL in clinical trials and disease management has become more prominent [47, 48]. Nonetheless, this escalation in research output has revealed heterogeneity in research methods, instruments, and conclusions. Given the absence of widely accepted QoL instruments for GD, and with only one such instrument currently in circulation, researchers have employed various QoL instruments to capture the salient constructs of interest, often with overlapping domains. GD is a rare disease, and its singular features are evident in the present study. Notably, the scarcity of patients with GD poses a challenge to patient recruitment [48, 49]. The majority of the studies incorporated in our review recruited patients via hospital-based clinical experts or patient groups. It is worth highlighting the considerable variation in patient numbers among the included studies, ranging from 3 to 212. Additionally, the heterogeneity of GD engenders marked inter-patient dissimilarities with regard to the clinical presentation, initial manifestations, and disease progression [50]. This variability is manifested in the diverse clinical presentation among the three GD types, as well as among patients of the same type with distinct underlying conditions. These factors have contributed directly to the observed discrepancies between patient experiences and self-reported outcomes. Furthermore, the scarcity of treatments for GD and ethical infeasibility of placebo groups necessitate the implementation of single-arm or pre-post-controlled trials, prompting judicious consideration of factors such as the sample size, patient demographics, age, and geographic location, as well as the instruments employed when interpreting and applying PROs results to GD patients. In this respect, attention must be focused on the most prevalent symptoms and effects that are of primary significance to patients, and which are expected to be alleviated or stabilized following treatment. The measurement of QoL in GD patients is dominated by generic instruments, and disease-specific scales are not sufficiently used. The GD1-PROM was developed based on patients from three countries, which largely expanded the number of patients included, ensured the quality of the cognitive interview, and avoided the omission of critical symptoms [21]. However, there may be differences between patients in different countries in terms of the genetic phenotype, language, culture, and perception of illness, which may also influence later administration of the scale. Currently only one of the two versions of the GD-PROM has been psychometrically validated; the other is applicable to routine monitoring in clinical practice and has not been validated. Finally, in some countries, a GD disease-specific scale cannot be directly applied because of language or cultural adjustment problems. In situations where the application of disease-specific scales is restricted, the use of a combination of symptom and generic scales may be a better solution. The inclusion of PROs in treatment trials for patients with GD has the potential to provide unique and valuable information to facilitate medical decision-making [51]. However, there are potential methodological challenges in the study design and implementation that must be adequately addressed. On the one hand, previous studies examining PROs in patients with GD have been predominantly cross-sectional or pre- and post-intervention investigations, and all three clinical trials have been open-label, with limited confidence in the conclusions drawn and a failure to effectively control for confounding factors. On the other hand, some studies have included patients without differentiation of subtypes, leading to a wide variation in results. Future studies must optimize the study design by utilizing a more uniform patient population and conducting subgroup analyses according to patient age and treatment intensity to ensure the accuracy of the assessment. Furthermore, the study design for PROs must also consider parent proxy responses and self-reporting of affected children. In instances where GD patients are too young or unable to complete self-reports because of illness or cognitive impairment, parents may be asked to report their child’s QoL through a parent proxy report. Studies on patients with GD, similar to those conducted on other rare [52, 53] and non-rare diseases [54, 55], have demonstrated moderate to good agreement between child self-reports and parent proxy reports. However, it is important to note that child’s and parent’s perceptions of the aspects of the disease affecting the QoL may differ. Therefore, future comprehensive assessments should incorporate both child and parent perspectives [56]. The application of PROs in GD has primarily focused on evaluating the current QoL and effectiveness of post-treatment interventions. However, more extensive applied studies, such as patient health utility values, satisfaction with treatment, and adherence to treatment, which contribute to drug development and marketing, are lacking. PROs are now widely used in the evaluation of new drugs, with 20% of new drug labels between 2006 and 2015 including PRO endpoints [47]. The fact that most rare diseases are chronic and require long-term intervention, and that clinical endpoints are not well-defined, highlights the value of PROs in rare diseases [48, 49]. In recent years, some countries and regions, such as the European Union and United States, have made increasing efforts to incorporate the patient voice into drug development. Between 2012 and 2016, orphan drug approvals by the European Medicines Agency and U.S. Food and Drug Administration were mainly focused on rare drugs, with 21.7% and 9.0% of all approved orphan drugs applying for PROs, respectively [57, 58]. Therefore, the use of PROs should be expanded to include studies of reported outcomes in patients with GD in order to better help patients in making decisions about disease management and health technology assessment. Conclusion The use of PROs in GD has been receiving increasing focus and attention, as evidenced by the upward trend in the number of studies conducted since 2016. Although a few disease-specific scales have been developed and validated, generic instruments such as the SF-36 are still primarily used for PROs assessment in GD. However, the measurement of QoL in GD is complicated by factors such as the small number of patients, disease heterogeneity, and cross-regional studies. To improve the measurement of patient QoL and treatment effectiveness, reliable and valid PROs instruments that reflect the unique experiences of patients with GD are needed. Ultimately, the incorporation of PROs in GD research and clinical practice can provide valuable insights for patients and healthcare professionals, supporting informed decision-making and improving patient outcomes. |
doc3 | What is Gaucher disease? Gaucher disease is a rare genetic disorder passed down from parents to children (inherited). When you have Gaucher disease, you are missing an enzyme that breaks down fatty substances called lipids. Lipids start to build up in certain organs such as your spleen and liver. This can cause many different symptoms. Your spleen and liver may get very large and stop working normally. The disease can also affect your lungs, brain, eyes, and bones. There are 3 types of Gaucher disease: Type 1. This is the most common type of Gaucher disease. It affects about 90% of people with the disease. If you have type 1, you don’t have enough platelets in your blood. This can make you bruise easily and feel very tired (fatigued). Your symptoms can start at any age. You might have an enlarged liver or spleen. You may also have kidney, lung, or skeletal problems. Type 2. This form of the disease affects babies by age 3 to 6 months. It is fatal. In most cases children don’t live beyond 2 years old. Type 3. Symptoms include skeletal problems, eye movement disorders, seizures that become more obvious over time, blood disorders, breathing problems, and liver and spleen enlargement. What causes Gaucher disease? Gaucher disease is passed down from parents to children (is inherited). It is caused by a problem with the GBA gene. It is an autosomal recessive disorder. This means that each parent must pass along an abnormal GBA gene for their child to get Gaucher. Parents may have only 1 GBA gene and, therefore, not show any signs of the disease, but be carriers of the disease. Gaucher disease type 1 is most commonly found among Ashkenazi Jews who have a high number of carriers of the defective GBA gene. What are the symptoms of Gaucher disease? Each person’s symptoms may vary. For many people, symptoms start in childhood. Some people have very mild symptoms. Symptoms of Gaucher disease can include: Enlarged spleen Enlarged liver Eye movement disorders Yellow spots in the eyes Not having enough healthy red blood cells (anemia) Extreme tiredness (fatigue) Bruising Lung problems Seizures How is Gaucher disease diagnosed? To make a diagnosis, your healthcare provider will look at your overall health and past health. He or she will give you a physical exam. Your provider will also look at: Your description of symptoms Your family medical history Blood test results Because Gaucher disease has so many different symptoms, it can take time to get an accurate diagnosis. How is Gaucher disease treated? There is no cure for Gaucher disease. But treatment can help you control your symptoms. Your treatment will depend on what type of Gaucher disease you have. Treatment may include: Enzyme replacement therapy, which is effective for types 1 and 3 Medicines Regular physical exams and bone density screening to check your disease Bone marrow transplant Surgery to remove all or part of your spleen Joint replacement surgery Blood transfusions What are the complications of Gaucher disease? Gaucher disease can cause other health problems such as: Delayed growth Delayed puberty Weak bones Bone pain Brain damage Joint pain Trouble walking or getting around Not having enough healthy red blood cells (anemia) Extreme tiredness (fatigue) What can I do to prevent Gaucher disease? If Gaucher disease runs in your family, talk with a genetic counselor. He or she can help you find out your risk of having the disease. You may also learn your chances of passing on the disease to your children. Testing the brother or sister of someone with Gaucher disease may help detect the disease early. This can help with treatment. When should I call my healthcare provider? Call your healthcare provider if you have any of these symptoms: Feeling dizzy Fainting Seizures Trouble breathing Loss of mobility Abnormal bone fractures or bone pain Call your provider if you have new symptoms, such as joint pain or seizures. Also let your provider know if your treatment is no longer helping to control your original symptoms. Living with Gaucher disease Follow your healthcare provider’s advice for taking care of yourself. Take your medicines as directed. Go to all of your follow-up medical visits. Key points It is a disorder passed from parents to children (inherited). It causes fatty substances called lipids to build up in certain organs such as the spleen and liver. Organs can become very large and not work well. It can also affect the lungs, brain, eyes, and bones. It can be hard to diagnose because there are many different symptoms. There is no cure, but treatment can help to control symptoms. Next steps Tips to help you get the most from a visit to your healthcare provider: Know the reason for your visit and what you want to happen. Before your visit, write down questions you want answered. Bring someone with you to help you ask questions and remember what your provider tells you. At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you. Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are. Ask if your condition can be treated in other ways. Know why a test or procedure is recommended and what the results could mean. Know what to expect if you do not take the medicine or have the test or procedure. If you have a follow-up appointment, write down the date, time, and purpose for that visit. Know how you can contact your provider if you have questions. |
doc4 | Gaucher (go-SHAY) disease is the result of a buildup of certain fatty substances in certain organs, particularly your spleen and liver. This causes these organs to enlarge and can affect their function. The fatty substances also can build up in bone tissue, weakening the bone and increasing the risk of fractures. If the bone marrow is affected, it can interfere with your blood's ability to clot. An enzyme that breaks down these fatty substances doesn't work properly in people with Gaucher disease. Treatment often includes enzyme replacement therapy. An inherited disorder, Gaucher disease is most common in Jewish people of Eastern and Central European descent (Ashkenazi). Symptoms can appear at any age. Products & Services A Book: Mayo Clinic Family Health Book Show more products from Mayo Clinic Symptoms There are different types of Gaucher disease, and signs and symptoms of disease vary widely, even within the same type. Type 1 is by far the most common. Siblings, even identical twins, with the disease can have different levels of severity. Some people who have Gaucher disease have only mild or no symptoms. Most people who have Gaucher disease have varying degrees of the following problems: Abdominal complaints. Because the liver and especially the spleen can enlarge dramatically, the abdomen can become painfully distended. Skeletal abnormalities. Gaucher disease can weaken bone, increasing the risk of painful fractures. It can also interfere with the blood supply to your bones, which can cause portions of the bone to die. Blood disorders. A decrease in healthy red blood cells (anemia) can result in severe fatigue. Gaucher disease also affects the cells responsible for clotting, which can cause easy bruising and nosebleeds. More rarely, Gaucher disease affects the brain, which can cause abnormal eye movements, muscle rigidity, swallowing difficulties and seizures. One rare subtype of Gaucher disease begins in infancy and typically results in death by 2 years of age. When to see a doctor If you or your child has the signs and symptoms associated with Gaucher disease, make an appointment with your doctor. Request an appointment Causes Autosomal recessive inheritance pattern Autosomal recessive inheritance pattern Enlarge image Gaucher disease is passed along in an inheritance pattern called autosomal recessive. Both parents must be carriers of a Gaucher changed (mutated) gene for their child to inherit the condition. Risk factors People of Eastern and Central European Jewish (Ashkenazi) ancestry are at higher risk of developing the most common variety of Gaucher disease. Complications Gaucher disease can result in: Delays in growth and puberty in children Gynecological and obstetric problems Parkinson's disease Cancers such as myeloma, leukemia and lymphoma |
doc5 | Gaucher disease is an autosomal recessive disease and the most prevalent lysosomal storage disorder with an incidence of about 1 in 20,000 live births. Despite the fact that GD consists of a phenotypic spectrum with varying degrees of severity, it has been subdivided in three subtypes according to the presence or absence of neurological involvement. It is also the most common genetic disease among Ashkenazi Jews, with a carrier frequency of 1 in 10 (Barranger and Ginns, 1989). This panethnic disease involves many organ systems (summarized in Table 1). The disease is highly variable as a consequence of modifier genes whose identities remain unknown. However, Gaucher disease is progressive in all of its forms. Genotype/ phenotype correlations are not reliable with the exception that the N370S allele, even if present in a single dose, protects from a neurodegenerative course (Tsuji et al., 1988). |
doc6 | Abstract Gaucher disease (GD, ORPHA355) is a rare, autosomal recessive genetic disorder. It is caused by a deficiency of the lysosomal enzyme, glucocerebrosidase, which leads to an accumulation of its substrate, glucosylceramide, in macrophages. In the general population, its incidence is approximately 1/40,000 to 1/60,000 births, rising to 1/800 in Ashkenazi Jews. The main cause of the cytopenia, splenomegaly, hepatomegaly, and bone lesions associated with the disease is considered to be the infiltration of the bone marrow, spleen, and liver by Gaucher cells. Type-1 Gaucher disease, which affects the majority of patients (90% in Europe and USA, but less in other regions), is characterized by effects on the viscera, whereas types 2 and 3 are also associated with neurological impairment, either severe in type 2 or variable in type 3. A diagnosis of GD can be confirmed by demonstrating the deficiency of acid glucocerebrosidase activity in leukocytes. Mutations in the GBA1 gene should be identified as they may be of prognostic value in some cases. Patients with type-1 GD—but also carriers of GBA1 mutation—have been found to be predisposed to developing Parkinson’s disease, and the risk of neoplasia associated with the disease is still subject to discussion. Disease-specific treatment consists of intravenous enzyme replacement therapy (ERT) using one of the currently available molecules (imiglucerase, velaglucerase, or taliglucerase). Orally administered inhibitors of glucosylceramide biosynthesis can also be used (miglustat or eliglustat). Keywords: Gaucher disease; lysosomal storage disease; glucocerebrosidase; GBA1 gene; enzyme replacement therapy; substrate reduction therapy; biomarkers 1. Introduction Lysosomal storage diseases (LSDs) are a group of heterogeneous inherited diseases caused by mutations affecting genes that encode either the function of the lysosomal enzymes required for the degradation of a wide range of complex macromolecules, but sometimes the function of specific transporters needed to export degraded molecules from the lysosomes. The resulting lysosomal dysfunction leads to cellular dysfunction and clinical abnormalities. In one group of LSDs, the sphingolipidoses, there is a dysfunction in the enzyme-degrading abilities of the metabolites which are essential components of cell membranes and regulators of various signaling pathways [1]. 2. Definition of Gaucher Disease Gaucher disease (GD, OMIM #230800, ORPHA355) is the most common sphingolipidosis. It was first described by Philippe Gaucher in 1882 in a patient with massive splenomegaly without leukemia. GD is a rare, autosomal, recessive genetic disease caused by mutations in the GBA1 gene, located on chromosome 1 (1q21). This leads to a markedly decreased activity of the lysosomal enzyme, glucocerebrosidase (GCase, also called glucosylceramidase or acid β-glucosidase, EC: 4.2.1.25), which hydrolyzes glucosylceramide (GlcCer) into ceramide and glucose (Figure 1A). More than 300 GBA mutations have been described in the GBA1 gene [2]. Very rarely, GD can also be caused by a deficiency in the GCase activator, saposin C [3]. The phenotype is variable, but three clinical forms have been identified: type 1 is the most common and typically causes no neurological damage, whereas types 2 and 3 are characterized by neurological impairment. However, these distinctions are not absolute, and it is increasingly recognized that neuropathic GD represents a phenotypic continuum, ranging from extrapyramidal syndrome in type 1, at the mild end, to hydrops fetalis at the severe end of type 2 [4]. Ijms 18 00441 g001 550 Figure 1. Hydrolysis of glucosylceramide (GlcCer) by glucocerebrosidase (GCase) in the lysosome (A). GCase is activated by saposin C. In lysosomal storage diseases, an enzyme deficiency is responsible for the accumulation of its substrate in the cell lysosome (overload disease). Gaucher disease is caused by a deficiency in glucocerebrosidase (GCase) (or β-glucosidase), which leads to an accumulation of GlcCer. GlcCer forms fibrillar aggregates that accumulate in macrophages and result in the cell cytoplasm presenting a characteristic “crumpled tissue paper” appearance (B), personal pictures, with the courtesy of Fabrice Camou and Rachid Seddik). These cells, known as Gaucher cells, infiltrate various organs (e.g., bone marrow, spleen, and liver) and are responsible for the major signs of the disease. 3. Epidemiology The disease’s incidence is around 1/40,000 to 1/60,000 births in the general population, but it can reach 1/800 births in the Ashkenazi Jewish population [5,6]. 4. Pathophysiology 4.1. Glucosylceramide Accumulation Mutations in the GBA1 gene lead to a marked decrease in GCase activity. The consequences of this deficiency are generally attributed to the accumulation of the GCase substrate, GlcCer, in macrophages, inducing their transformation into Gaucher cells. Under light microscopy, Gaucher cells are typically enlarged, with eccentric nuclei and condensed chromatin and cytoplasm with a heterogeneous “crumpled tissue paper” appearance (Figure 1B). This feature is related to the presence of GlcCer aggregates in characteristic twisted, fibrillar arrangements that can be visualized using electron microscopy [7]. Gaucher cells mainly infiltrate bone marrow, the spleen, and liver, but they also infiltrate other organs and are considered the main protagonists factors in the disease’s symptoms. The monocyte/macrophage lineage is preferentially altered because of their role in eliminating erythroid and leukocytes, which contain large amounts of glycosphingolipids, a source of GlcCer. GlcCer accumulation in Gaucher cells is considered the first step towards bone involvement, leading to the vascular compression which is the source of necrotic complications [8]. The pathophysiological mechanisms of neurological involvement remain poorly explained; GlcCer turnover in neurons is low and its accumulation is only significant when residual GCase activity is drastically decreased, i.e., only with some types of GBA1 mutations [9]. Consistent with this, recent work on a Drosophila model of neuronopathic GD demonstrated autophagy impairment in the GCase-deficient fly brains [10]. Very rarely, GD may be caused by a mutation in the PSAP gene, leading to a deficiency in saposin C without GCase deficiency [3]. These patients generally present with neurological features similar to that of type-3 GD. 4.2. Subpopulation of Gaucher Cells, a Specific Cell Subpopulation Recent observations indicate that Gaucher cells do not only result from the transformation of macrophage cells, but correspond to a distinct M2 subpopulation from an alternative differentiation pathway [11]. There are many functional states of macrophage polarization, and they can be fully polarized and acquire a specific phenotype like M1 (characteristic macrophage activation) or M2 (alternative macrophage activation). These specific phenotypes depend on the tissue and specific microenvironment where the macrophages are. The M2 subpopulation has been described as cells with anti-inflammatory, immunomodulatory and tissue repair properties, and includes macrophages that remove abnormal hematopoietic cells or phagocytose erythroblast nuclei. The in vivo situation appears more complex since the plasma cytokine profile and the characteristic monocytes circulating in the blood show concurrent activation of inflammatory M1 macrophages, presumably implicated in the “pseudo-inflammatory” state that was described many years ago and in the heterogeneous manifestations of the disease [12,13]. Thus numerous cytokines, chemokines and other molecules—including IL-1β, IL-6, IL-8, TNFα (Tumor Necrosis Factor), M-CSF (Macrophage-Colony Stimulating Factor), MIP-1β, IL-18, IL-10, TGFβ, CCL-18, chitotriosidase, CD14s, and CD163s—are present in increased amounts in Gaucher patients’ plasma and could be implicated in hematological and bone complications [14,15,16,17]. Only some of these molecules are expressed by Gaucher cells themselves. This is the case for chitotriosidase and CCL18, which thus constitute quite specific disease biomarkers [11]. Osteoporosis may be linked to IL-10, which inhibits osteoblast activity, but also to IL-1β, IL-6 and M-CSF, MIP-1α and MIP-1β, which stimulate bone resorption by increasing osteoclast activity [14,17]. The relationship between Gaucher cells located in tissues and developed from M2 macrophages and blood monocytes with an M1 phenotype is still not understood, and this distinction should be maintained. 4.3. Metabolic Consequences Other Than Accumulation of Glucosylceramide in Gaucher Cells Due to the accumulation of GlcCer, Mistry et al. identified another metabolic pathway in a mouse model [18] (Figure 2A). GlcCer is also the substrate of an alternative pathway in which a ceramidase transforms it into glucosylsphingosine (or Lyso-glucosylceramide), which then diffuses into fluids due to its reduced hydrophobicity. This pathway is favored in cases of GCase deficiency. In the cytoplasm, glucosylsphingosine is metabolized by a second GCase that is active at a neutral pH (GBA2 gene), producing sphingosine and then sphingosine-1-phosphate (S1P) [19,20]. Sphingosine could be particularly toxic to bone; in this model, deletion of GBA2 could reverse the Gaucher disease phenotype, particularly the bone abnormalities. In addition, the accumulation of glucosylsphingosine may cause neuronal dysfunction and death, leading mainly to GD-related neurological symptoms [21]. Glucosylsphingosine is normally absent from the human brain, but it is detectable in the brains of patients with GD-related neurological lesions, even if Gaucher cells are not observed in their nervous system. Glucosylsphingosine could represent a more specific and sensitive biomarker than chitotriosidase or CCL18 [19,22]. Glucosylsphingosine could serve as a source of S1P, influencing the differentiation, migration, and survival of several cell types, including lymphocytes and macrophages [23]. Ijms 18 00441 g002a 550Ijms 18 00441 g002b 550 Figure 2. Alternative metabolic pathway of the glucosylceramide (GlcCer) accumulation due to the glucocerebrosidase (GCase) deficiency. The expression of GCase varies from one cell type to another and depends on the tissue. (A) In a mouse model of GCase deficiency (red cross), GlcCer is transformed via an alternative ceramidase pathway into glucosylsphingosine (red arrow), which is degraded by cytoplasmic GCase2 (GBA2 gene), active at a neutral pH, to S1P, a very active metabolite [20]. (B) Protein maturation takes place in the Golgi apparatus; the transport and delivery of GCase to lysosomes require a particular molecule, LIMP-2, which allows GCase to reach the lysosome where the acidic pH breaks the molecular link [39]. (C) LIMP-2 is a lysosomal membrane protein (LMP) whose highly glycosylated intra-lysosomal part protects the lysosome’s membrane. LIMP-2 anomalies can induce a phenotype rather than GD3 [39]. It has been demonstrated that the enzyme deficiency may have an impact on many cells, including hematopoietic progenitor cells, erythrocytes or mesenchymal cells [24,25,26], hepatocytes [27] and the nerve cells of patients with neurological lesions. 4.4. Abnormalities in the Intracellular Trafficking of Glucocerebrosidase The enzymatic deficit of GCase is not only due to the intrinsic enzymatic dysfunction but is also the consequence of abnormalities occurring during the transport and delivery of the enzyme to the lysosomes. Thus, enzyme misfolding during its passage through the endoplasmic reticulum can lead to its premature degradation by the proteasome [28,29] (Figure 2B–C). The transport and delivery of GCase to the lysosome does not depend on the mannose 6-phosphate system, like other proteins, but also involves Lysosomal Integral Membrane Protein 2 (LIMP-2) [30]. GCase linked with LIMP-2 is inactive. The acidic milieu of lysosomes promotes this delinking, allowing its activation. LIMP-2 mutations (SCARB2 gene) have been described in several neurological disorders [31,32]. LIMP-2 mutations can affect the GD phenotype [33]. It seems that while LIMP-2 deficiency alone does not cause the observed phenotype, it is probably an important modifier of GD, potentially turning a patient with type-1 GD into a type-3 [33]. SCARB2 mutations could explain GD heterogeneity in the context of the same mutation of GCase. Other molecules could be involved in this trafficking pathway of GCase, such as progranulin. Progranulin is an indispensable co-chaperone that links GCase/LIMP2. The serum level of progranulin is significantly lower in GD patients than in healthy controls, and this leads to GCase accumulation in the cytoplasm [34]. The loss of progranulin leads to abnormal endothelial reticulum trafficking and the aggregation of various proteins in the cytoplasm, such as GCase/LIMP2, which increase degradation of GCase [35]. An insufficiency of PGRN has also been associated with many types of neurodegenerative disease, including frontotemporal dementia, Parkinson’s disease (PD), Alzheimer's disease, multiple sclerosis, and amyotrophic lateral sclerosis [36]. It has been observed that patients with the same GCase mutations may vary significantly in disease presentation, from life-threatening to almost asymptomatic [37,38], because of molecular co-abnormalities. This helps us to understand the phenotypic heterogeneity of GD. 4.5. Relationship between the GBA1 Gene and Parkinson’s Disease Patients with a heterozygous (or homozygous) mutation in the GBA1 gene, especially c.1226A>G (N370S), but also c.1448T>C (L444P), c.84dup, c.115+1G>A (IVS2+1G>A), c.1297G>T (V394L), and c.1604G>A (R496H), are now considered at risk for Parkinson’s disease (PD) [40,41,42]. However, all GBA mutations including null alleles seem to increase the risk for PD [43]. The onset of PD tends to be earlier in patients carrying null or recombinant alleles [44]. The prevalence of heterozygous mutations is found to range from 3% to 8% in Caucasian PD [42,43] and is higher in the Ashkenazi Jewish population, reaching 15% or even 31% [40,43]. The most recent studies suggest that neuropathic mutations of the GBA gene (especially c.1448T>C (L444P)) could worsen the progression of PD [45,46]. Loss of GCase function compromises lysosomal α-synuclein degradation and causes accumulation of oligomers. It results in neurotoxicity through accumulation in the substantia nigra of the brain. GlcCer, the GCase substrate, directly influences amyloid formation of α-synuclein by stabilizing soluble oligomers, which then aggregate and form Lewy bodies in the nerve cells in PD [47]. These α-synuclein polymers have an inhibitory effect on GCase [47,48,49], engendering a vicious circle (Figure 3). The effect of GBA1 gene mutations could be modulated by the co-activator of GCase, saposin C, which may partly explain the limited penetrance of neurological impairment in patients with GD [50,51]. GCase deficiency has been implicated in non-GBA1 linked PD, and interaction between GCase and other molecules involved in PD pathophysiology has been described [52,53]. GCase levels decrease with age in non-PD patients and GCase is decreased in idiopathic PD as well as GBA1-linked PD. Ijms 18 00441 g003 550 Figure 3. Relationship between glucocerebrosidase (GCase) and neurological diseases with Lewy bodies. (A) Normally, GCase interacts with its substrate glucosylceramide (GlcCer) as well as monomers of α-synuclein in lysosomes, facilitating the breakdown of both at acidic pH; (B) Mutated GCase or decreased levels of GCase result in a slowdown of α-synuclein degradation and a gradual build up of GlcCer, with the formation of α-synuclein oligomers and fibrils [48,49,54]; GlcCer stabilizes the α-synuclein oligomers [47]. These oligomers are able to bind to the mutated GCase molecules and inhibit the enzymatic activity of GCase, further decreasing the enzyme activity [47,50,55]. These impaired lysosomes show impaired chaperone-mediated autophagy and autophagosome fusion. This results in an increased accumulation of α-synuclein in the cytoplasm, forming insoluble aggregates to form Lewy bodies. These aggregates block trafficking of GCase from the endoplasmic reticulum (ER) to the Golgi [56]. Mutant GCase is retained in the Endoplasmic reticulum, which causes ER stress and evokes the ER stress response (Unfolded Protein Response) [57]. Saposin C can have a modulating effect on this by binding to GCase and thus maintaining its activity [51,58]. 4.6. Relationship between GCase Deficiency and Neoplasia The frequency of hypergammaglobulinemia and the presence of monoclonal Ig in GD are two factors which promote the emergence of multiple myeloma; the incidence of myeloma appears to be increased in GD, with a relative risk of at least 5.9 (95% CI: 2.8–10.8) [59,60,61,62]. There is also an increased relative risk of lymphoma [61,63] and of solid cancer (hepatocellular carcinoma [62], melanoma, and pancreatic cancer [63]), but there is less evidence than for hematological cancers. The pathophysiology of cancer development in GD is not well understood. At least two types of mechanisms may be operating, both of them relating to the GCase deficiency and the ensuing catabolic defect, i.e., the accumulation of GlcCer and/or its deacylated product, glucosylsphingosine or Lyso-glucosylceramide (LGL1) [64]. The most common hypothesis is that the (perturbed) cellular and cytokinic microenvironment in GD is responsible for tumorigenesis: perturbations include markedly elevated levels of some cytokines and chemokines [14,15,16,17], activated (M2) macrophages [11], abnormal responses by T lymphocytes, and a reduction of NK cells [65,66]. The second hypothesis considers that initial steps towards a catabolic defect originate not from the environment, but from the (future) malignant cell itself. Facilitation of tumorigenesis in GD could be related to the disturbed sphingolipid metabolism in cancer cells, due to GlcCer (or glucosylsphingosine) accumulation or reduced ceramide formation, resulting in deleterious changes in the pro- and anti-proliferative balance [64]. Recently, a murine model of GD with a long-term development of B cell malignancies has been investigated [67]. Interestingly, mice bearing large tumors had less GlcCer and glucosylsphingosine accumulation than those with small tumors. In this model, the monoclonal protein disappeared from mice treated with eliglustat; moreover, a striking reduction in lymphoproliferation was observed, with no plasmocytoma or lymphoma [68]. A more recent study on monoclonal immunoglobulin (Ig) in GD showed that in 17 of 20 patients with GD and six of six Gaucher mice, the clonal Ig was specific for glucosylsphingosine. Given that myeloma plasma cells showed evidence of antigen-driven selection and that there is increased risk of MGUS and myeloma in GD, it was tested whether immunoglobulin was reactive to LGL1 and lysophosphatidylcholine. In 33% of sporadic monoclonal gammopathies, the clonal Ig was specific for the two targets. Thus, extended exposure of the immune system to high levels of LGL1 and lysophosphatidylcholine might favor gammapathies and myeloma [69]. This observation suggests that LGL1 could be a relevant predictive biomarker and should be further studied in this context. Moreover, treating the above murine model of GD with eliglustat led to a reduction of clonal Ig. The glucosylsphingosine might mediate B-cell activation in GD and might indeed be the antigenic origin of GD-associated monoclonal gammopathy. These new data give glucosylsphingosine a key role in myeloma or lymphoma in GD [69]. 4.7. Altered Iron Metabolism Iron is stored in ferritin to avoid toxicity to cell components. In GD, ferritin levels in Gaucher cells are higher and the synthesis of hepcidin, which inhibits intestinal absorption of iron, is increased. In Gaucher cells, certain cytokines (IL-6 and IL-1β) also increase hepcidin gene transcription; the macrophages activated in this way can also induce iron retention via an autocrine mechanism [70] and decrease glycosylation capabilities, leading to a decrease in glycosylated ferritin [71]. Hyperferritinemia in type-1 GD is associated with indicators of disease severity [72], and ferritin could be a useful though nonspecific biomarker; it is also an inflammation marker. 5. Clinical Presentations Gaucher disease is characterized by hepatosplenomegaly, cytopenia, sometimes severe bone involvement and, in certain forms, neurological impairment. The variability in the clinical presentations of GD may be explained by the continuum of phenotypes [73]. However, three major phenotypic presentations can usually be distinguished. They are described below, in order of increasing severity. Type-1 GD is usually named non-neuronopathic GD; type-2 and type-3 are termed neuronopathic-GD. 5.1. Type-1 Gaucher Disease (ORPHA77259) Type-1 GD (GD1), usually distinguished by the absence of neurological impairment, is the most common form of the disease (prevalence: 90%–95% in Europe and North America). Its clinical presentation is variable, ranging from asymptomatic throughout life to early-onset forms presenting in childhood. The initial symptoms vary considerably and patients can be diagnosed at any age [6]. Depending on the study, the median age of diagnosis is from 10 to 20 years old [6,74]. Although the overall mean onset of patients in the Gaucher Registry (run by the International Collaborative Gaucher Group) is at 20.4 years old, the majority (56%) of patients experienced onset before 20. However, this Registry primarily includes symptomatic and treated patients, and thus the mean age is probably skewed. Two thirds (68%) of this group were diagnosed before 10 years old and almost half (48%) before the age of 6 [75,76]. GD1 can often limit quality of life and is often associated with considerable morbidity, but is rarely life threatening. Fatigue is common (50% of patients) and often has an impact on school life or socio-professional activities. In children, growth retardation and delayed puberty are common (growth <5th percentile in 34% of children) [75]. Splenomegaly is observed in more than 90% of patients and is sometimes massive, with a spleen weighing up to several kilograms and causing abdominal pain or distension. Indeed, it may be the only clinical sign, leading to unnecessary tests if GD is not considered. Splenic infarction may complicate matters; spleen rupture only occurs very rarely [77,78]. Hepatomegaly is noted in 60%–80% of patients. The development of fibrosis and subsequent cirrhosis is rare [6]. Hepatic and splenic infarction may be observed, manifesting with acute pseudo-surgical abdominal pain. Up to 40% of GD1 patients have a focal lesion in the liver and/or spleen. A gaucheroma is the most likely diagnosis, but a hepatocellular carcinoma or a lymphoma of the spleen are other possible diagnoses. Gaucheromas have varied imaging characteristics and it is therefore difficult to distinguish a gaucheroma from another lesion [79]. The prevalence of gallstones in GD1 is 32%, i.e., five times higher than in the general population [27]. Bile analyses reveal cholesterol stones and GlcCer. Bleeding phenomena may be observed at diagnosis. These are rarely severe and usually related to thrombocytopenia (60%–90% of cases) or to coagulation or primary hemostasis disorders [80] or, more rarely, to platelet disorders [81]. Mucocutaneous bleeding (epistaxis, gingival bleeding, menorrhagia, etc.) is common; postoperative hemorrhage or bleeding during birth and spontaneous hematomas (e.g., psoas hematomas) have also been reported. Anemia, observed in 20%–50% of cases, is generally moderate. Leukopenia is rare. Bone involvement causes acute pain manifested as very painful bone crises, predominantly in the pelvis and lower limbs (more rarely in the upper limbs), and/or chronic pain that should be assessed using a visual analog scale or digital scale [82]. The severity of the pain varies, but it may have an impact on functional prognosis. The pathophysiology of bone manifestations is poorly known and justifies the use of common terminology. The painful bone crises are probably associated with ischemic vaso-occlusive phenomena. It seems that they may be reversible and do not show up as lesions in medical imaging. However, they usually cause abnormalities referred to as bone infarcts on long bones (metaphyses or diaphyses) and flat bones, and lesions referred to as avascular necrosis (AVN) on the epiphyses. In addition to the vascular theory explaining the ischemic events (bone infarcts and AVN), a mechanical theory has also been put forward to explain the spontaneous or trabecular microfractures that are observed (mechanical or spontaneous AVN), particularly on the femoral head, the femoral condyle and the tibial plateau. The pathophysiological mechanism can involve other potential factors, such as alterations in the bone marrow or immune cells, inflammation, macrophage-derived factors, cytokines, and hormones [83,84]. Acute painful bone crises are more common in children (30% of children with GD1). They usually progress over 7–10 days and are associated with local inflammation, mild fever (38 °C), polynuclear leukocytosis and a moderate inflammatory syndrome. These symptoms are similar to osteomyelitis (pseudo-osteomyelitis), thus sometimes delaying diagnosis [82,85]. AVN is observed in 15% of cases, most often at the femoral or humeral heads, more rarely at the femoral condyles or tibial plateaus, and exceptionally in the feet (talus, calcaneus), hands and the spine (vertebra plana). In the long term, AVN may be complicated by osteoarthritis, often justifying joint replacement surgery [72]. Bone crises are predictive of future bone infarcts and AVN. Bone infarcts with clinical consequences, AVN and pathological fractures are considered as severe bone complications of GD and are defined as bone events [72]. Moderate losses of bone mass (osteopenia) or more severe declines (osteoporosis) increase with age and menopause in normal subjects. Loss of bone mass occurs earlier and is more severe in patients with GD and may cause pathological fractures (of long bones, vertebrae, etc.). Bone mass decline seems to be correlated with other bone and visceral complications [86]. Focal lytic lesions that can erode the cortical bone and promote pathological fractures are sometimes observed in different locations (long bones, jaw, etc.) [87]. Cyst-like lesions in the mandible, with the loss of trabecular structure, may lead to dental abnormalities. Extra-osseous extension of Gaucher cells secondary to the destruction of the cortical bone only occurs very rarely [88]. Secondary bone tumors including osteosarcomas or osteoblastomas have been reported very rarely [89,90]. When magnetic resonance imaging (MRI) is not available, standard radiographs may be used to observe bone remodeling disorders with enlargement of the metaphyseal/diaphyseal region of the femur’s lower part, referred to as the Erlenmeyer flask bone deformity, appearing during childhood [91]. The sequelae of AVN and bone infarction, thinning of the cortical bone, focal lysis, fractures and osteoarthritis can also be observed. Radiographs may also be used to monitor patients after joint replacement surgery. MRI is the reference examination and is used to objectify bone marrow infiltration (80% of cases) at a very early stage, as well as bone infarcts, AVN and bone lysis. Bone marrow infiltration and Erlenmeyer flask bone deformities do not seem to correlate with the other bone complications [92]. Pulmonary involvement may be related to infiltration of the lungs by Gaucher cells, creating an interstitial disease that can lead to pulmonary fibrosis, restrictive lung disease secondary to spinal deformation, or pulmonary arterial hypertension [93,94]. The latter is more common in splenectomized patients, particularly women, or may be caused by hepatopulmonary syndrome complicating hepatic cirrhosis. Pulmonary involvement is rare in all GD phenotypes and seems more frequent in patients homozygous for the 1448G (L444P) mutation [95]. Rarely, renal involvement, manifested as proteinuria and hematuria, reflects infiltration of glomeruli by Gaucher cells [96]. Skin involvement is manifested as yellow-brown hyperpigmentation, usually on the anterior parts of the tibias and cheeks [97]. Ocular manifestations such as vasculitis [98,99] or vitreo-retinal involvement with whitish spots (corresponding to glucoceramide deposits) [98,100], myocardial or valvular involvement [101], insulin resistance [102] and amyloidosis [103,104,105] are observed very rarely. Contrary to the conventional definition of GD1, certain neurological manifestations associated with this phenotype have been described in recent years. Patients with GD1 have an increased risk of developing Parkinson’s disease (4–20 times greater), often at an earlier age than in normal PD [43,47,106,107]. The prevalence of minimally symptomatic peripheral neuropathies and small fiber neuropathies is 14% and therefore higher than in the general population [108]. 5.2. Type-3 Gaucher Disease (ORPHA77261) Also called juvenile or subacute neurological GD, the type-3 form (usually 5% of cases, but up to 33% in some cohorts [109]) exhibits the visceral manifestations described in GD1, usually combined with oculomotor neurological involvement, which appears before 20 years of age in most cases. Like GD1, GD3 phenotypes are very heterogeneous, particularly with regard to neurological involvement. Some patients present moderate systemic involvement with horizontal ophthalmoplegia as the only neurological symptom, whereas others present more severe forms with varying neurological signs including progressive myoclonus epilepsy (16% of patients), cerebellar ataxia or spasticity (20%–50% of patients), and dementia in some cases [110,111]. Neurological signs may occur several years after the visceral manifestations, even in patients initially identified and treated as having GD1. Disease onset is more common in young children, with neurological symptoms appearing before 2 years of age in half the cases [110]. Behavioral changes and unexpected death are described in some patients [112]. Spinal surgery may be required for the sometimes severe and progressive kyphosis that may develop, through an unknown mechanism, despite specific GD treatment. Cardiac involvement (with valve calcification) [113], corneal involvement and hydrocephaly are reported mainly in patients with GD3 of the c.1342G>C (D409H) genotype [114]. Subjects with the very rare saposin C deficiency almost always present with neurological impairment comparable to that observed in GD3 [115]. 5.3. Type-2 Gaucher Disease (ORPHA77260) Type-2 GD (<5% of cases in most countries, but up to 20% in some cohorts [109]) is characterized by early and severe neurological impairment starting in infants aged 3–6 months old and by systemic involvement with hepatosplenomegaly. The triad consisting of rigidity of the neck and trunk (opisthotonus), bulbar signs (particularly severe swallowing disorders), and oculomotor paralysis (or bilateral fixed strabismus) is very suggestive of the disease. These signs may be associated with trismus and hypertonia with pyramidal and possibly extrapyramidal rigidity [116]. Apnea related to increasingly frequent and lengthy laryngeal spasms occurs after a few months. Psychomotor development is then altered, although some children may still continue to acquire skills. Seizures occurring later manifest as myoclonic epilepsy that is resistant to antiepileptic drugs. Splenomegaly is almost always present, associated with thrombocytopenia in 60% of cases. Growth retardation (30% of patients) may be the first sign, sometimes associated with cachexia. Lung lesions are sometimes also observed, resulting from repeated aspirations and pulmonary infiltration by Gaucher cells. There is no bone involvement in GD2. Death occurs before the third year of life, following massive aspiration or prolonged apnea [116,117]. The mean survival age of GD2 is 11.7 months (range 2–25 months), and pulmonary symptoms (GD-pneumopathy) and aspiration caused by Gaucher disease or the aggravation of respiratory conditions such as central apnea are the cause of 50% of fatal cases [116]. Fetal GD is the rarest (<1%) and the most severe form of the disease. It usually manifests with hydrops fetalis, hepatosplenomegaly, ichthyosis, arthrogryposis, facial dysmorphia and fetal thrombocytopenia. Death often occurs in utero or soon after birth [118]. The diagnosis of these fetal forms is particularly important for appropriate genetic counseling and the possibility of offering a prenatal diagnosis in future pregnancies. 6. Diagnosis of Gaucher Disease The diagnosis of GD often takes place several years after the onset of the first clinical and laboratory signs. This is a typical problem with rare diseases characterized by a progressive onset of symptoms. 6.1. GCase Activity The diagnosis of GD must be confirmed by establishing deficient GCase activity in total leukocytes or mononuclear cells, or cultured fibroblasts. The residual enzyme activity is usually approximately 10%–15% of the normal value [119]. Dried blood spots can also be used for the enzymatic assay, but any potential deficiency should be confirmed using the previous method. Flow cytometry analysis of blood monocytes is a more accurate method [26,120], but it has not been validated by different centers. The very rare saposin C deficiency should be tested for when GCase activity is normal but the clinical picture and biomarkers point to GD and especially when chitotriosidase activity is very high. The diagnosis is made by PSAP gene sequencing. 6.2. Bone Marrow Aspiration Bone marrow aspiration is not mandatory to confirm a diagnosis of GD, but it may be performed on patients without a diagnosis when isolated thrombocytopenia and/or splenomegaly are found and it can help when Gaucher cells are found. However, bone marrow aspiration should not routinely be performed in GD. Very rarely, it may be impossible to use cytology for diagnosis when only a few cells are available. In addition, it may be difficult to distinguish Gaucher cells from the so-called “pseudo-Gaucher” cells observed in some blood disorders or infectious diseases, such as myeloma with histiocytic accumulation of immunoglobulin crystals [121], Waldenstrom’s disease and other lymphomas with monoclonal gammopathy [122], chronic myeloid leukemia or myelodysplasia [123,124], or atypical mycobacteria [125]. 6.3. GBA1 Mutations The gene encoding GCase (GBA1) is located on the long arm of chromosome 1 (1q21) and it contains 11 exons. The presence of a highly homologous pseudogene (GBAP) at the same locus (16 kb downstream) is responsible for recombination events between GBAP and GBA1 (e.g., RecNciI allele) [126]. More than 400 mutations have been described in the GBA1 gene, but some of them are more common, such as c.1226A>G (N370S), c.1448T>C (L444P), c.84dup, c.115+1G>A (IVS2+1G>A) and RecNciI [127]. The mutations most prevalent (90% of the mutant alleles) in Ashkenazi Jewish GD1 patients are c.1226A>G, c.84dup, c.1448T>C and c.115+1G>A, whereas they account for about 60% of total mutations in non-Ashkenazi patients. The c.1226A>G (N370S) mutation is rarely seen in Asian and Arab populations and mutant allele frequencies are very different. The c.1226A>G (N370S) mutation is particularly common in the Ashkenazi Jewish population (about 75%–80% of the alleles), but it accounts for only 30% of the alleles in non-Jewish patients. The presence of the c.1226A>G (N370S) mutation in a homozygous or heterozygous state excludes the risk of neurological involvement (GD2 or GD3), but it does not predict the severity of bone and visceral involvement. Patients homozygous for the N370S mutation can remain asymptomatic for a long time, whereas those homozygous for the L444P mutation are at a high risk of developing neurological impairment (GD2 or GD3). Homozygotes for the rare c.1342G>C (D409H) mutation present characteristic heart valve damage [114]. Patients carrying two null mutations (leading to a total absence of glucocerebrosidase activity) do not survive beyond the perinatal period (fetal forms incompatible with life) [76]. 6.4. Prenatal Diagnosis Prenatal diagnosis of GD can be performed by genetic analysis, using either chorionic villus sampling (sampled at 10–12 weeks of amenorrhea) or amniotic fluid cells (as early as 16 weeks of amenorrhea), but only if the index case genotype has been previously identified [128]. It can also be done by measuring glucocerebrosidase activity on fresh chorionic villi or cultured amniotic cells. 7. Laboratory Abnormalities 7.1. Hemogram Thrombocytopenia of varying degrees is common (90% of cases): <60 × 109 platelets/L in 26% of cases; <120 × 109 platelets/L in 76% of cases [74]. Anemia is less common (56% of cases) and moderate, with hemoglobin levels rarely found to be less than 9 g/dL; leukopenia is rare. Cases of GD without thrombocytopenia are observed. These cytopenias are attributed to splenic sequestration and bone marrow infiltration, but a direct impact of the enzyme deficiency on immature hematopoietic cells has also been described [26,129]. The blood count may be normal in patients with a history of splenectomy. Immune thrombocytopenias have been described. 7.2. Hemostasis Several hemostatic abnormalities have been described in GD, including prolonged prothrombin time (PT) and activated partial thromboplastin time (APPT). These could possibly be related to deficiencies in factor X, factor V, thrombin (or a more global deficiency), factor XI (common among Ashkenazi Jews) or vitamin K. They could also be related to deficiencies secondary to liver failure (rare in GD) or to potentially associated genetic or even acquired von Willebrand disease [130]. However, the relationship with potential signs of bleeding is not obvious, especially as platelet disorders are common [131]. 7.3. Proteinemia, Serum Immunofixation and Electrophoresis These examinations must be carried out to screen for polyclonal hypergammaglobulinemia (25%–91% of cases) and possible monoclonal gammopathy (1%–35% of cases) [132,133]. Specific treatment reduces polyclonal hypergammaglobulinemia, but seems to have a limited effect on monoclonal gammopathy [134]. 7.4. Disease Biomarkers Currently, the most interesting biomarkers are chitotriosidase, CCL18, glucosylsphingosine and ferritin. Chitotriosidase is produced in large quantities by Gaucher cells, and it has been used as a biomarker since 1994 [135]. Its level is generally very high without treatment, so it can be used to monitor treatment efficacy and is considered to have some prognostic value [136]. However, chitotriosidase levels can vary considerably among patients; indeed, a mutation (24-bp duplication) in the CHIT1 gene leads to total deficiency (homozygosity for the mutation) in 6% of the general population and chitotriosidase activity is low and difficult to interpret in a third of patients with a heterozygous mutation. In practice, these limitations hamper its use for between-patient comparisons [137]. Furthermore, different techniques used for the assessment of chitotriosidase levels prevent the comparison of results between centers. Increased chitotriosidase levels are also observed, but to a lesser extent, in certain other lysosomal storage diseases (e.g., Niemann–Pick diseases) and a variety of non-LSD disorders (sarcoidosis [138], β-thalassemia, multiple sclerosis, Alzheimer’s disease, or visceral leishmaniasis [139]). CCL18 is a chemokine produced by various cell types, particularly macrophages (mainly of the M2 type) and dendritic cells [140]. CCL18 promotes the recruitment of T lymphocytes through CCR8 [141]. Gaucher cells produce CCL18 and it is found at high levels in plasma. CCL18 levels may also be increased in chronic inflammatory diseases such as idiopathic pulmonary fibrosis, some cancers and scleroderma; it is generally a bad prognosis [142,143]. Its levels are also increased in allergic reactions, insulin resistance and obesity. In GD patients, CCL18 plasma levels are 10–50 times higher than those of controls [11,144,145]. Its levels vary less than those of chitotriosidase since there is no genetic polymorphism; the kinetics of CCL18 and chitotriosidase are generally similar at treatment induction. High levels of CCL18 are associated with a poorer prognosis. It is essential to evaluate its level in patients with chitotriosidase deficiency. A standardization of the CCL18 assay should also be done before comparing data from different centers. Glucosylsphingosine is a novel biomarker whose sensitivity and specificity are superior to those of chitotriosidase and CCL18 [19,22]. It was recently shown to be very valuable for patient monitoring [146,147,148], but has yet to be assessed on a larger scale. Assays are recommended at the same frequency as the other biomarkers. All three biomarkers—chitotriosidase, CCL18, and glucosylsphingosine—are closely related within the context of GD: they vary in the same direction and are generally correlated [148]. Ferritinemia is higher than normal in most GD patients (>85%), while serum iron, transferrin saturation and soluble transferrin receptor concentrations remain normal [149]. High levels of iron reserves accumulate preferentially in the liver and bone marrow. Ferritin levels may be predictive of the onset of bone complications and are frequently associated with splenectomy [72]. The ferritin level should therefore be monitored in GD (even if it is a non-specific marker), as should increased inflammation (by monitoring for normal levels of C-reactive protein). Phlebotomy is theoretically not indicated for hyperferritinemia in GD; patients can be tested for associated hemochromatosis if transferrin saturation is high [150]. More accurate techniques, such as flow cytometry, can be used to quantify GCase enzyme activity in specific cell populations. This method is more sensitive because it is possible to focus the GCase assay on monocytes, where the level of enzyme is markedly higher than in other cells. This can reveal activities of the order of only 10% of normal activity [26,120]. The enzyme level could be used as a biomarker for treatment management. The oldest biomarkers of GD are tartrate-resistant acid phosphatase (TRAP) and angiotensin converting enzyme (ACE). Their lack of specificity and the availability of more specific biomarkers have rendered them less useful today [151]. 7.5. Others Biological Tests Liver function tests (e.g., free and conjugated bilirubin, transaminases, alkaline phosphatase, gamma GT) are not usually abnormal but may be carried out, sometimes revealing cholestasis (increase in alkaline phosphatase, bilirubin, and gamma-GT), but rarely cytolysis (increase in transaminases). C Reactive Protein (CRP) levels may be high in bone crises (bone infarction) or infectious complications (cholecystitis more common in GD). Measurement of serum calcium (potentially serum phosphorus) and vitamin D is recommended. Vitamin D deficiency seems to be more common in GD than in the general population and supplementation is highly recommended when the 25(OH)D level is less than 75 nmol/L [152]. Auto-antibodies (antinuclear, anti-phospholipid antibodies) have been found in GD patients, usually without clinical signs, but are not routinely tested for. Antibodies directed against the therapeutic enzyme (imiglucerase) are detected in 2%–14% of cases, but are of no consequence in practice. They are only assayed in the case of an allergic reaction or a loss of treatment efficacy [153]. Some bone remodeling markers can be assayed: in theory, a decrease should be observed in bone formation markers (e.g., osteocalcin), whereas bone resorption markers (such as ICTP for C-terminal type-I collagen telopeptide) should be normal or higher, but the published studies are discordant [84]. Compared to control subjects, GD1 patients showed decreased HDL-cholesterol and ApoA1 levels, with increased triglyceride levels, however, there was no difference in the mean carotid intima-media thickness between GD patients and control subjects (not leading to premature atherosclerosis) [154]. 8. Radiological Investigations Abdominal magnetic resonance imaging (MRI) is the most appropriate examination for assessing liver and spleen dimensions (organ volume) and morphology. The spleen sometimes presents nodules suggestive of lymphoma. When MRI is unavailable or in cases of uncontrollable claustrophobia, an abdominal ultrasound may be used instead. Computed tomography (CT) has previously been used for estimating Gaucher organ volumes; nonetheless, MRI, because of justifiable concerns about CT radiation, is preferable because repeat assessments are routinely required [155]. Bone magnetic resonance imaging (MRI) is the test of choice for evaluating the effects of GD on bone. Bone marrow infiltration is predominant at the proximal and distal ends. T1 weighted sequences are recommended to detect and quantify bone marrow infiltration, while T2 weighted sequences are used to detect complications such as AVN or bone infarction [156]. Hypointense signals are generally observed in T1 weighted sequences, reflecting the replacement of normal bone marrow fat by Gaucher cells. Infiltration may be quantified by means of the various scores used in reference centers, such as the Bone Marrow Burden score [157,158]. Assessment of bone marrow infiltration is more difficult in children due to the presence of red bone marrow in the long bones. Magnetic resonance imaging is used to assess the extent of lesions and whether complications are recent (edema due to recent infarction) or longstanding. Other types of MRI are used for semi-quantitative assessments of bone marrow infiltration (Quantitative Chemical Shift Imaging), but they are not available in all centers [159]. Whole-body MRI makes it possible to reduce examination time, particularly for disease monitoring purposes. The images must be carefully analyzed because additional images are sometimes required for the less visible sites, especially limb extremities (hands and feet). Standard osseous radiographs were previously used to detect Erlenmeyer flask deformity of the femurs with widening of the lower third. This can be accompanied by thinning of the cortical bone (which may appear scalloped [160]), AVN and bone infarct sequelae (34% of cases), lytic lesions (18% of cases) that are generally well delineated without peripheral increased bone density, and the sequelae of traumatic or pathological fractures. The initial assessment should include radiological imaging of the pelvis, spine, femurs, tibiae, and humeri. Radiological imaging need not be systematically reused thereafter for monitoring purposes, except for specifically following the progression of AVN to osteoarthritis. The sensitivity of standard radiological imaging for the detection of abnormalities in GD is low [156] and the use of multiple X-rays is no longer standard practice given the limited knowledge gained from them and risk of radiation exposure. Bone densitometry is used to diagnose osteopenia/osteoporosis, which is common in adults or children >5 years old, and to calculate lumbar spine and femoral bone mass. Osteopenia is defined as a T score between −1 and −2.5; osteoporosis is defined as a T score ≤ −2.5. The severity of osteopenia may be correlated with genotype, splenomegaly and hepatomegaly [86]. 99mTc bone scintigraphy is sometimes used to locate bone lesions throughout the skeleton (especially the spine, femur, pelvis or tibia) when MRI is not available [161]. It enables the detection of clinically asymptomatic lesions or the sequelae of bone infarcts in atypical sites (jaws, hands or feet), as well as fractures. Echocardiography is used to screen for pulmonary arterial hypertension. 9. Management 9.1. Usual Specific Treatments All GD patients require regular monitoring, however specific medication is not justified in all cases. Once it has been initiated, treatment must generally be administered for life. There are currently two specific types of treatment for GD: enzyme replacement therapy (ERT) and substrate reduction therapy (SRT). The goal is to treat patients before the onset of complications, the sequelae of which are disabling or not improved by further treatment, including massive fibrous splenomegaly, AVN, secondary osteoarthritis, vertebral compression and other fractures, hepatic fibrosis and lung fibrosis. 9.1.1. Enzyme Repacement Therapy The principle of ERT is to supply the GCase lacking in the cells, particularly the Gaucher cells. After using an enzyme extracted from human placenta (alglucerase) in the early 1990s, Genzyme SA developed imiglucerase, a recombinant GCase (Cerezyme®, Sanofi-Genzyme). Enzymes are deglycosylated, exposing their mannose residues in order to allow their uptake by macrophage receptors and their transfer to lysosomes. Imiglucerase is produced using mammalian cells (Chinese Hamster Ovary cells); it obtained marketing authorization in 1996. Other recombinant enzymes have now been developed: velaglucerase (Vpriv®, Shire, authorized in 2010) produced using human fibroblasts and taliglucerase (Elelyso®, Pfizer) produced using carrot cells, which was available during a period of imiglucerase shortage (2009–2011), but did not obtain a marketing authorization in all countries. The differences between imiglucerase and velaglucerase are minimal. Taliglucerase undergoes specific glycosylation, related to its production in plant cells. These products are administered intravenously. Dose and administration frequency vary depending on the country [162], often with individual adjustments of dosages. For children and “at risk adults”, a starting dose of 60 U/kg every other week (EOW) has been recommended [163]. After the achievement of therapeutic goals [164] this may be reduced to not less than 30 U/kg EOW to prevent worsening skeletal involvement during long-term maintenance therapy [163]. Some studies have reported good outcomes with low-dose high-frequency protocols, consisting of 15–30 U/kg/month given in thrice weekly doses [165,166]. Smaller total doses can decrease the cost of therapy and can be considered for patients with stable GD1 [167,168]; however, 15 U/kg EOW or lower doses may compromise skeletal response in some patients [168,169]. For many years, there was considerable debate about the optimal ERT dose, but dose–response relationships were demonstrated for hemoglobin and platelet levels, and for hepatic and splenic volumes [170]. To fully appreciate how an individual is affected by GD and how that individual is responding to treatment, it is necessary to evaluate all aspects of the disease: blood counts, organ volumes, quality of life, bone pain and crises, bone remodeling, marrow fat and bone mineral density. Assessment of growth in children, with reference to both their age- and sex-matched cohort and their mid-parental height, is also very important [171]. The dose, and less frequently the interval, of infusions can be adjusted according to the clinical course and biomarkers. Thrombocytopenia usually improves with ERT, but it may persist in individuals with residual splenomegaly and/or the presence of splenic nodules [172]. Individuals with type-1 GD report improved health-related quality of life after 24–48 months of ERT [173,174,175]. Bone marrow infiltration and osteopenia regress gradually with ERT [176]; bone pain improves, there are fewer bone crises [177], and occurrences of skeletal events decrease [178], although ERT does not completely prevent them [6]. Early treatment with ERT reduces the risk of AVN [179]. Disease control with low doses remains poorly understood but may be related to specific intracellular pharmacokinetics [120]. There are currently no criteria for the preferential use of one or other of the enzyme replacement therapies (imiglucerase or velaglucerase) to treat GD1; imiglucerase is the only ERT with a marketing authorization for GD3. None of the ERTs are indicated for GD2 as treatment has no impact on the rapid progression of its severe neurological symptoms [116]. There is no evidence that ERT has reversed, stabilized, or slowed the progression of neurological involvement [180]. Specific treatment with ERT should be considered for all GD3 patients, but only for those GD1 patients who have symptomatic clinical or biological abnormalities [163]. Safety is generally good: From 2% to 14% of patients (depending on the product) develop antibodies against the enzyme, usually without clinical signs. Allergic reactions are rare (<1.5% of patients) and include urticaria, diarrhea, hypotension or laryngeal discomfort. The risk of allergy seems a little more common with taliglucerase. Pregnancy is not a contraindication to imiglucerase replacement therapy since no fetal malformations have been described in pregnant women for whom treatment continued. Velaglucerase also appears to be well tolerated [181]. Indeed, ERT may be required, firstly to control the disease, since GD can worsen during pregnancy, and secondly to limit thrombocytopenia which can be harmful during pregnancy or childbirth and contraindicates epidural anesthesia. 9.1.2. Substrate Reduction Therapy The aim of substrate reduction therapy (SRT) is to reduce excess cell GlcCer by decreasing its production. Miglustat (Zavesca®, Actelion) is a GlcCer synthase inhibitor which reduces the biosynthesis of GlcCer in Gaucher cells. It obtained a European marketing authorization in November 2002 for the treatment of mild to moderate GD1 when ERT is not suitable [182]. Miglustat is effective on the size of the liver and spleen as well as on the decrease of chitotriosidase levels, however its efficacy on hematological parameters is more limited and improvement takes longer (improvement of anemia after 24 months, little improvement of thrombocytopenia). Its efficacy on bone symptoms remains poorly evaluated. Miglustat is administered orally at the recommended dose of 100 mg, three times daily, but doses may need to be progressively increased at treatment initiation to improve tolerance. Miglustat can produce side effects (diarrhea, weight loss, hand tremors or possible peripheral neuropathy) although these generally regress with dose reduction or treatment discontinuation. Diarrhea can be effectively controlled with loperamide and certain dietary measures (limiting the consumption of disaccharides in the form of sugars and milk) [183]. Miglustat is a second-line treatment to be used when ERT is no longer accepted by the patient or cannot be used due to intolerance. It is strictly contraindicated during pregnancy and contraceptive methods must be used by both male and female patients. To date, miglustat has not been found to have any effect on neurological symptoms in GD3, despite the fact that it crosses the blood–brain barrier. Another substrate inhibitor, eliglustat (Cerdelga®, Sanofi-Genzyme) was granted a marketing authorization in 2015. It is also an orally administered GlcCer synthase inhibitor, but is more specific and more potent than miglustat, because it is an analogue of the ceramide part. It was evaluated in phase-1, -2 and -3 clinical studies comprising nearly 400 patients overall whose follow-up results were published after four years [184,185,186,187]. The studies demonstrated significant efficacy versus placebo, non-inferiority to imiglucerase (the reference product) over a two-year period and satisfactory safety. The four-year extension phase of the phase-2 study also demonstrated that it had an effect on bone [188]. This drug is suggested as first-line treatment for patients with GD1. Due to potential drug–drug interactions, its use with CYP2D6 inhibitors calls for special caution, depending on the patient’s metabolizer status (CYP2D6 genotyping required before any prescription). Eliglustat is indicated for the long-term treatment of adults with GD1 who are cytochrome 2D6-poor, intermediate or extensive metabolizers (determined previously). It is not indicated for use in ultra-extensive metabolizers. Eliglustat is not recommended in patients with pre-existing cardiac disease (e.g., congestive heart failure, recent acute myocardial infarction, bradycardia, heart block, ventricular arrhythmia, long QT syndrome), and in concomitant use with Class 1A and Class III antiarrhythmics. Adverse effects are uncommon and usually mild, including headache and pain in limb extremities in less than 10% of cases. Given that it is metabolized by cytochrome P450, certain drug–drug interactions should be anticipated. Eliglustat offers eligible patients a daily oral therapy alternative to biweekly infusions of ERT [189]. 9.2. Other Specific Treatments Ideally, bone marrow transplantation could cure patients with GD [190], but this treatment is no longer offered given its low benefit/risk ratio and the current availability of effective, well-tolerated therapies. 9.2.1. Gene Therapy A preliminary gene transfer protocol was used on GD3 patients [191], with the aim of introducing the GBA1 gene into hematopoietic cells and then injecting the corrected cells into patients. Results were disappointing as the GCase levels proved too low for any clinical effect. Lentiviral vector gene transfer techniques have been used in mouse models of GD with promising results, but this approach is still at the basic research stage [192]. 9.2.2. Molecular Chaperones Molecular chaperones are small molecules that enable proteins to take on the specific molecular configuration which determines their functional efficacy. They also protect proteins by preventing inappropriate aggregation, that facilitate their passage through the cell membranes and thus their transport into lysosomes, when dealing with lysosomal enzymes. Molecular chaperones can therefore help the production of functional enzymes and thus even restore the intracellular activity of mutant GCase [193]. The development of this type of treatment for GD is still in the early stages, and clinical trials have yet to be conducted, although the strategy is under consideration [194]. The effect is thought to be responsible for the positive results of pilot studies with ambroxol [195,196]. 9.3. Symptomatic Treatments In the era of ERT, splenectomy should be avoided in GD patients. The potential consequences of splenectomy include the usual risks of infection, thrombosis or neoplasia [197] as well as a risk of worsening the GD [198] due to an increased risk of skeletal-related events, hepatic fibrosis, cirrhosis, hepatic carcinoma and pulmonary hypertension. Splenectomy should only be performed in exceptional circumstances and considered only in rare cases of non-response to well conducted ERT with persistent severe cytopenia (usually related to massive nodular and fibrous splenomegaly) or in cases of splenic rupture. The usual recommendations for splenectomy should be followed (pre-vaccination and antibiotic prophylaxis). Painful bone crises often require temporary immobilization and use of level I and II analgesics, sometimes even level III. Specific treatment typically reduces the frequency and intensity of these crises [199]. The use of bisphosphonates is controversial in GD because the pathophysiology of bone mass decline remains poorly understood. It appears to be the consequence of either an osteoclast or osteoblast disorder or, more likely, of an osteoblast–osteoclast coupling disorder. Specific therapy remains the best treatment for GD-related osteopenia and osteoporosis. Bisphosphonates are nonetheless often indicated in cases of persistent osteoporosis, especially in postmenopausal women. They are contraindicated during childbearing age [198]. Orthopedic surgery may be required for bone complications including AVN and pathological fractures. Except in the context of an emergency, it is preferable to operate on patients after a correction of their laboratory parameters, particularly thrombocytopenia. Liver transplantation may be proposed for the rare patients presenting with severe liver disease progressing to fibrosis and liver failure. To prevent bleeding, GD patients should be evaluated for coagulation abnormalities, especially prior to surgery, dental and obstetric procedures. Psychological support should be routinely offered to GD patients and they should be put in touch with patients’ associations. 10. Monitoring Patient monitoring includes regular clinical, biological and radiological evaluations. ERT improves hematological abnormalities and quality of life within a few months [200]. Biomarker levels (chitotriosidase, CCL18 and ferritin) decrease relatively quickly with ERT, prior to the normalization of platelet and hemoglobin levels [201]. Hepatosplenomegaly decreases more slowly, usually over a period of two years. Improvement of bone abnormalities is usually observed after 2–4 years of treatment, but some abnormalities remain irreversible (hepatic or splenic fibrosis, AVN and bone infarction sequelae, etc.). A significant proportion of patients show improvement, but without normalization of their cytopenia or organomegaly [202]. GD3 patients require additional neurological monitoring. Pediatric patients are monitored more frequently: a clinical examination and full battery of laboratory tests must be carried out every six months and imaging is used as a function of disease progression. 11. Prognosis Currently, available treatments make it possible to reduce cytopenias and organomegalies and to significantly decrease bone manifestations, considerably improving a patient’s quality of life. Outcomes may be unfavorable due to aggressive, irreversible and disabling bone disease, despite specific treatment (bone events can occur despite treatment in some patients); due to the onset of Parkinson’s disease and Lewy body dementia; or the occurrence of a blood disease or cancer (hepatocellular carcinoma), whose relative risk appears higher in GD. When ERT is ineffective in patients with GD3, progressive neurological deterioration has an impact on their prognosis. Moreover, GD3 patients can die suddenly [112]. The outcome is always fatal for patients with type 2 GD. 12. Conclusions Although it is the most common of the lysosomal storage diseases, Gaucher disease remains rare and most cases present a gradual onset phenotype, which explains its delayed diagnosis. It is important to include GD in the diagnostic decision tree in cases of splenomegaly and/or thrombocytopenia, in order to avoid potentially harmful splenectomy. Significant new insights into GD’s pathophysiology show that GCase deficiency has a much broader impact than the simple macrophage load that transforms them into Gaucher cells. These insights will open new pathways for the development of innovative therapeutic strategies. Eventually, drugs that can modify the neurological phenotype are expected to be developed. It is likely that more complex molecular studies will ultimately contribute to customized patient management. The therapeutic advances of recent years, including the development of new enzymes and a new substrate inhibitor, represent significant progress, but research efforts must be maintained. Patients with GD, including asymptomatic patients, must be monitored regularly to detect any complications in the disease’s progression. Abbreviations AVN Avascular Necrosis ERT Enzyme Replacement Therapy GCase glucocerebrosidase GlcCer glucosylceramide GD Gaucher Disease SRT Substrate Reduction Therapy |
doc7 | Abstract Incidence and prevalence estimates for Gaucher disease (GD) are scarce for this rare disease and can be variable within the same region. This review provides a qualitative synthesis of global GD incidence and prevalence estimates, GD1–3 type-specific and overall, published in the last 10 years. A targeted literature search was conducted across multiple databases from January 2011 to September 2020, including web-based sources and congress proceedings to May 2021. Searches yielded 490 publications, with 31 analyzed: 20 cohort studies (15 prospective, 5 retrospective), 6 cross-sectional studies, 5 online reports (most from Europe (n = 11) or North America (n = 11); one multiregional). Across all GD types, incidence estimates ranged 0.45–25.0/100,000 live births (16 studies), lowest for Asia-Pacific. Incidence of GD1: 0.45–22.9/100,000 live births (Europe and North America) and GD3: 1.36/100,000 live births (Asia-Pacific only). GD type-specific prevalence estimates per 100,000 population were GD1: 0.26–0.63; GD2 and GD3: 0.02–0.08 (Europe only); estimates for GD type unspecified or overall ranged 0.11–139.0/100,000 inhabitants (17 studies), highest for North America. Generalizability was assessed as “adequate”or “intermediate” for all regions with data. GD incidence and prevalence estimates for the last 10 years varied considerably between regions and were poorly documented outside Europe and North America. Data for GD2 and GD3 were limited. Keywords: Gaucher disease; incidence; prevalence; real-world data 1. Introduction Gaucher disease (GD) is among the most prevalent of the lysosomal storage disorders (LSDs), a group of over 70 inherited metabolic diseases with a combined frequency of ~1:5000 live births [1]. Specifically, the incidence of GD in the general population has been estimated previously at between 0.39 and 5.80 per 100,000 live births [2], and also at 1.5 (95% confidence interval [CI] 1.0–2.0) per 100,000 live births [3]. Prevalence estimates for GD per 100,000 population included the range from 0.70 to 1.75 [2] and 0.9 (95% CI 0.7–1.1) [3]. GD is an autosomal recessive LSD caused by mutations in the GBA1 gene encoding the glucosylceramide-degrading enzyme β-glucocerebrosidase [4]. Accumulation of glucosylceramide in macrophages leads to a range of clinical manifestations of varying severity and age of onset, classified into three clinical types: GD1–3 [5]. Across the broad phenotypic spectrum of GD, clinical presentations can include splenomegaly, hepatomegaly, and blood and bone abnormalities; these are typical of GD1 (the type affecting > 90% of patients with GD from Europe and North America). Neurologic symptoms are distinctive of GD2, an acute and severe neurologic form of the disease, and GD3, a chronic neurologic form [6,7]. Delayed diagnosis or misdiagnosis of GD commonly occurs on account of the complex clinical presentation of this multisystem disorder, coupled with a lack of awareness about this rare disease [8,9,10]. Patient outcomes can be improved by timely administration of enzyme replacement or substrate reduction therapies early in the disease course [11,12,13]; conversely, delays to the initiation of appropriate therapy can lead to irreversible health damage [10,13]. Prevalence reflects the estimated number of patients with GD in the population of a country/region at a given time (point prevalence) or period (period prevalence), and incidence is the occurrence of new cases of GD occurring in a population over a particular period of time. GD incidence is associated with ethnicity and is known to be higher in particular populations, such as those of Ashkenazi Jewish descent (estimated at 1 in 450 births for GD type 1) and a population from the Norrbotten and Västerbotten geographical areas of Sweden (estimated at 1 in 50,000 births for GD type 3) [9,14,15]; however, GD affects all ethnic groups and prevalence is likely to be underestimated in many countries [16,17]. Newborn screening programs were developed for several LSDs, aiming to achieve earlier disease detection with a view to improving long-term patient outcomes [18,19,20]. Heterogeneity among the epidemiological estimates for GD can be a result of studies focusing on local ethnic groups or on particular health-seeking study populations. There is a need for a better understanding of the global incidence and prevalence of GD, together with an evaluation of incidence rates for specific ethnic populations found within each geographic region. This will help achieve better forecasting of disease burden and improve the evaluation of treatment provision. The objective of this targeted review was to provide a qualitative synthesis of global GD incidence and prevalence estimates by region, overall, and by disease type, published in the last 10 years. 2. Methods 2.1. Literature Searches The methodology for this targeted literature search was derived from the National Academy of Medicine standard [21]. Publications in English indexed in the MEDLINE and EMBASE databases were searched from 1 January 2011 to 30 September 2020. The search strategies combined search terms for the population of interest (patients with GD of any type) with outcomes of interest (incidence and prevalence). The geographical scope of the review was worldwide, although there was a particular focus on the GD3 type in the Asia-Pacific region when outputs were screened; however, this focus did not influence the search strategy. If no recent, generalizable estimates were found for the parameter (incidence or prevalence) and region, pragmatic searches were conducted to identify additional sources where needed. If no estimates were found or if the generalizability of available estimates was graded as “poor”, pragmatic searches were conducted for data from which incidence and/or prevalence estimates could be derived (i.e., studies reporting on the number of patients with GD and the time period). Additional sources included: OpenGrey (the system for information on the gray literature in Europe), The Grey Literature Report (produced by the New York Academy of Medicine), and Orphanet (portal for rare diseases and orphan drugs in Europe). The search strategy used was based on disease of interest (“Gaucher disease” OR “Gaucher disease type 1” OR “Gaucher disease type 2” OR “Gaucher disease type 3”) combined with outcomes of interest (“incidence” OR “prevalence”). Other web-based sources were also searched, which included relevant societies and congress proceedings (last date searched: 6 May 2021) as well as the citations from retrieved publications (search methodology termed “snowballing”). Country-specific incidence or prevalence was estimated using the number of patients with GD and size of catchment population matched for the time period. Where possible, estimates were standardized to per 100,000 for comparison purposes. 2.2. Study Selection Publications retrieved from searches were screened for eligibility by a single assessor in a two-stage process based on prespecified eligibility criteria (Table 1). Stage 1 screening: after removal of duplicates, title and abstracts from the literature search outputs (published from 2011 onwards) were manually screened against the study eligibility criteria (Table 1A). Stage 2 screening: search outputs retained after Stage 1 screening underwent in-depth full-text review to confirm eligibility using Patient, Intervention, Comparator, Outcomes, Time period, Setting (PICOTS)-based criteria (Table 1B). Table 1. Publication eligibility criteria. Table The generalizability of incidence and prevalence estimates to a region was graded (“adequate,” “intermediate,” or “poor”) on the basis of prespecified criteria related to population coverage, the number and size of countries within a given region, and the characteristics and size of the study population (Table 2). Table 2. Rules to assess regional generalizability of estimates. Table Following the screening process, eligible publications underwent standardized data extraction by a single assessor using a data extraction form (the initial pilot was carried out by two independent assessors). Quality control checks for screening and data extraction were performed by a second assessor on a random sample of 10% of studies. A qualitative and narrative synthesis of estimates was provided for each epidemiologic parameter of interest (incidence and prevalence). Findings were reported according to GD type and country or region of interest, when available. There was no pooling of estimates or derivation of weighted averages. 3. Results 3.1. Search Outputs Stepwise screening of outputs from the literature search, with reasons for exclusion, were documented in a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow chart (Figure 1). Jcm 12 00085 g001 550 Figure 1. PRISMA flow chart. * Pragmatic searches yielded 13 web-based sources and two additional outputs identified from snowballing search methodology (referring to the use of reference lists or citations from identified sources to find additional sources). PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Initial searches identified 475 publications from MEDLINE and EMBASE; 395 underwent Stage 1 eligibility screening following duplicate removal, and 47 were retained for in-depth Stage 2 eligibility screening, which excluded a further 31 publications. With 15 additional sources (13 web-based, two identified by snowballing search methodology) identified from pragmatic searches, a total of 31 outputs were retained for data extraction: 20 cohort studies (15 prospective and five retrospective), six cross-sectional studies, and five online reports (Figure 1). Following quality control checks of the publication screening and data extraction processes, inter-assessor agreement was 92.5%. Publications most commonly involved ad hoc data collection in prospective cohort studies (n = 12, 38.7%) and disease registries (n = 12, 38.7%). The majority of studies were from Europe (n = 11, 35.5%) or North America (n = 11, 35.5%), and one study was multiregional [22]. 3.2. GD Incidence In the studies that were identified and included in this review, the incidence was defined as either the number of new diagnoses of the disease during the study period divided by the total births in the same period (i.e., birth incidence), or the number of newly diagnosed cases among hospital visits or in the general population. Global incidence estimates for any GD type per 100,000 live births ranged from 0.45 to 25.0 (data from 13 prospective studies [23,24,25,26,27,28,29,30,31,32,33,34,35], two retrospective cohort studies [36,37], and one newsletter from a National GD registry [38]). Most sources covered Europe (n = 7, 41.2%) and North America (defined as the USA and Canada; n = 7, 41.2%), then the Asia-Pacific region (n = 2, 11.8%). For the majority of studies, incidence estimates appeared to be derived from a general population of mixed ancestry rather than from specific populations, except for two estimates from the USA, one confirmed as being from a population of Ashkenazi Jewish ethnicity (22.9) [33] and another from a health-seeking population (20.0) [30]. The majority of incidence estimates were for unspecified GD, five estimates were GD type-specific, and one was for GD overall. Data from newborn screening programs contributed 13 of the 17 estimates of GD incidence from 16 studies: four out of seven estimates from Europe (4.5 [23], 5.76 [31], 7.5 [34], and 7.82 [32]), seven out of eight estimates from North America (0.45 [25], 1.42 [27], 1.59 [35], 2.27 [25], 2.29 [28], 22.9 [33], and 25.0 [24]) and both incidence estimates from Asia-Pacific (1.24 [29] and 1.36 [26]). In general, lower GD incidence estimates were reported in the Asia-Pacific region compared with Europe and North America. Incidence estimates from North America and Europe were considered of intermediate generalizability to those regions, while estimates from Asia-Pacific were of adequate generalizability. Incidence estimates by GD type were all based on data from newborn screening programs and included estimates for GD1 incidence (0.45–22.9/100,000 live births) from four studies: three from North America and one from Europe. The estimate for GD3 (1.36/100,000 live births) was from one study in the Asia-Pacific region [26] (Table 3, Table 4 and Table 5, Figure 2). Jcm 12 00085 g002 550 Figure 2. Summary of GD incidence estimates by country and region. GD unspecified refers to absence of any mention of whether study targeted GD overall or a given type. * For the eight data points from the USA (in ascending order), the corresponding time periods of study were: 2014–2016; 2017 †; 2016 †; 2014–2016; 2013; 2020 †; 2013–2017; 2010–2011. † Year of publication of the study. 3.2.1. Europe Incidence estimates for Europe (from seven studies) ranged from 2.0 to 7.82/100,000 live births for GD (unspecified GD type or overall). Three out of seven incidence estimates (5.76 [31], 7.50 [34], and 7.82 [32]) contributing to the range were from newborn screening programs and the generalizability of the estimates was graded as intermediate because data were included from three out of the five designated countries: France, Italy, and Spain (Table 3). GD1 incidence (4.5/100,000 live births [23]) was reported by one study from Northern Italy from a newborn screening program. 3.2.2. North America Incidence estimates for any GD type (eight estimates from seven studies) were highly variable, ranging from 0.45 to 25.0/100,000 live births; seven out of eight incidence estimates were from newborn screening programs. GD1 incidence (0.45 to 22.9/100,000 live births) was reported by three studies from newborn screening programs. Incidence estimates for GD (excluding GD type-specific estimates) were 1.42 to 25.0/100,000 live births; four out of six estimates (1.42 [27], 2.27 [25], 2.29 [28], and 25.0 [24]) contributing to this range were from newborn screening programs. The generalizability of the estimates to North America was graded as intermediate as the data included were from the USA and not Canada (Table 4). 3.2.3. Asia-Pacific The incidence estimate for GD (unspecified) from one study in China was 1.24/100,000 live births [29]; GD3 incidence was reported by one study from Taiwan (1.36/100,000) [26]. Both estimates were from newborn screening programs and generalizability of the estimates was graded as adequate (data from China included) [26,29] (Table 5). 3.3. GD Prevalence All of the studies that were identified and included in this review examined standard prevalence as the number of patients with GD per 100,000 general population. Global prevalence estimates for any GD type per 100,000 population ranged from 0.02 to 139.0 (data from two prospective studies [39,40], four retrospective cohort studies [37,41,42,43], six cross-sectional studies [22,42,44,45,46,47], and five reports [38,48,49,50,51]). Most sources (n = 6) provided prevalence estimates for European populations, followed by those from North America (n = 4), Latin America (n = 3), and the Middle East (n = 3); one study provided multiregional data [22]. There were no prevalence estimates for the Asia-Pacific region. The majority of prevalence estimates were for unspecified GD; there were six estimates for GD overall and eight GD type-specific estimates. The highest single prevalence estimate (139.0) was for an Ashkenazi Jewish population in North America [40], whereas the lowest was 0.02 from one study on GD2 [47] and one study for GD3 [44], both from Europe. GD type-specific prevalence estimates were only available for Europe (Figure 3, Figure 4 and Figure 5 and Supplemental Tables S1 and S2). Jcm 12 00085 g003 550 Figure 3. Prevalence estimates for GD: Europe. Data sourced from cross-sectional studies unless otherwise stated. One study contributing prevalence data was multiregional. Some studies reported prevalence estimates for more than one GD type. GD unspecified refers to absence of any mention of whether study targeted GD overall or a given type. Estimates from source reference [22] except France [37]; Spain GD unspecified (2020) [38]; Spain and Portugal GD overall (2012) [46]; Romania [44]; Russia [47]; UK [21]. * Retrospective cohort study of the Russian population aged > 18 years 2006–2016 [47]. † Estimates were calculated using the reported prevalence and distribution of GD types. ‡ Estimates were calculated using the country population size during the study period. § Year of publication. ∥ Cross-sectional study of the Romanian population in 2017 [44]. ¶ Retrospective cohort study of the French population in 1980–2015 [37]. ¦ Society report of UK population in 2016 [21]. Jcm 12 00085 g004 550 Figure 4. Prevalence estimates for GD: North America. GD unspecified refers to absence of any mention of whether study targeted GD overall or a given type. * Source: Cerdelga® notice of refusal in Quebec population in 2017 [51]. † Estimates were calculated using the country population size during the study period. ‡ Retrospective cohort study in adult Ontario population in 2016 [43]. § Estimates were calculated using the reported prevalence and distribution of GD types. ∥ Source: Physician’s guide to Gaucher Disease from NORD US population in 2013 [50]. ¶ Prospective cohort of Ashkenazi Jewish students participating in an at-home national Jewish genetic disease screening initiative [40]. Jcm 12 00085 g005 550 Figure 5. Summary GD prevalence estimates by country and region. GD unspecified refers to absence of any mention of whether study targeted GD overall or a given type. * Year of publication. † Study reported prevalence estimates for more than one GD type and GD overall. 3.3.1. Europe Estimates for the prevalence of any GD type per 100,000 population ranged from 0.02 to 1.1 (seven publications). Regional generalizability of the estimates was graded as adequate because they included all of the five prespecified countries (France, Germany, Italy, Spain, and UK). Prevalence estimates for unspecified GD (excluding estimates for GD1–3) ranged from 0.11 to 1.1 per 100,000 population. Prevalence of GD1 ranged from 0.26 [47] to 0.63 [37] per 100,000 population. The lowest prevalence estimates were type-specific for GD2: 0.02 [47] to 0.08 [37] and GD3: 0.02 [44,47] to 0.04 [47] (Figure 3). 3.3.2. North America Prevalence estimates for any GD (from four studies) ranged from 0.60 to 139/100,000 population. The two highest estimates (139.0 [40] and 10.15 [43]) were both from Ashkenazi Jewish populations: one from a US prospective cohort study reporting results from saliva-based GD screening of Ashkenazi Jewish adults [40] and the second from a retrospective chart review of adults with at least one GD specialist consultation from a GD referral center in Ontario, Canada with GD detection using β-glucocerebrosidase activity in leukocytes or fibroblasts [43] (Figure 4). Generalizability of the estimates was graded as adequate because data were included from Canada and the USA. Prevalence of GD that was unspecified or overall (excluding the two estimates from Ashkenazi Jewish populations) ranged from 0.60 [51] to 1.93 [50]/100,000 population. Prevalence estimates were also available for Latin America: 0.15 [41] to 0.32 [39] (four estimates from three studies [39,41,48]) and were considered of adequate generalizability (data included from three of the four named countries: Argentina, Brazil, Colombia; no data from Mexico). Prevalence estimates for the Middle East were 0.20 [45] to 20.2 [52] (six estimates from four studies [22,42,45,52]) and were of intermediate generalizability (data included from two of the four named countries: Iran and Israel; no data from Egypt or Turkey). There were no prevalence estimates for the Asia-Pacific region. 4. Discussion This targeted literature review provides a global overview of GD incidence and prevalence estimates from the past 10 years, together with an evaluation of the generalizability of these estimates to each region studied. Global incidence estimates for GD overall (any GD type from 16 studies) ranged from 0.45 to 25.0 per 100,000 live births, with the data mostly derived from cohort studies in Europe and North America (two studies from Asia-Pacific). Data on GD incidence were scarce in the literature, and GD type-specific estimates in particular were found in only five studies: four for GD1, none for GD2, and one for GD3. Based on prespecified criteria, the regional generalizability of incidence estimates was considered intermediate for North America and Europe and adequate for the Asia-Pacific region. For any GD, incidence estimates for North America (0.45–25.0) were higher than for Europe (2.0–7.82) and Asia-Pacific (1.24–1.36). The global incidence range was also higher and more variable than reported in a previous qualitative literature review (0.39 to 5.80 per 100,000 births), which included data from 10 national cohort-based studies conducted in general populations of mixed ancestry [2]. A quantitative synthesis of published data pooled from 16 studies calculated GD birth prevalence as 1.5 cases (95% CI 1.0–2.0) per 100,000 live births, with a higher value for Europe (n = 8 studies; 1.7 [95% CI 1.0–2.3]) compared with North America (n = 4 studies; 1.3 [95% CI 0.2–2.4]) [3]. After removal of two of the highest incidence estimates from North America identified from health-seeking populations [30] or those of Ashkenazi Jewish descent [33] from our study, one of the higher estimates for incidence of 25.0 per 100,000 births could not be excluded on either of these grounds. However, without this estimate, a range of 0.45–7.82 for global GD incidence would be more in line with the previous qualitative literature review [2]. Of note, the 25.0 estimate was derived from a pilot blood spot screening program for LSD in Illinois, USA, where two cases of unspecified GD were identified from sampling 8012 newborn infants over 6 months [24]. The study authors conceded that data were inconclusive for some infants and recommended second-tier testing and long-term follow-up to address high false-positive rates reported from pilot LSD screening programs [25,27,53]. The majority of estimates of GD incidence (13 of 17) were from newborn screening programs, including the three highest GD incidence estimates from Europe (5.76, 7.50, and 7.82). Variability found in the incidence estimates within regions can be attributed to data derived from specific, health-seeking populations or from studies of particular GD carrier populations being set alongside studies from the general population and data from newborn screening programs [18,19]. All these sources of variability were applicable to the data collected for North America in this review. Identification of GD in newborn screening programs was largely reliant on assays detecting reduced β-glucocerebrosidase activity in dried blood samples collected from newborn infants, determined by tandem mass spectrometry [23,31,33,34]. Other methods included liquid chromatography tandem mass spectrometry [31] and the digital microfluidic enzyme assay [28]. The methodology for identifying GD varied and was not provided for all newborn screening programs. Studies comparing different methodologies for analyzing β-glucocerebrosidase activity in dried blood specimens together with GBA gene sequencing of the same patient samples have highlighted several analytical variables affecting data reliability [54,55], such that a shift to GD diagnosis based on glucosylsphingosine (lyso-Gb1) measurements and GBA mutation analyses has been proposed [56]. General criticisms of data from pilot newborn LSD screening programs related to the reporting of high incidence rates [27] that were not predictive of disease phenotype. These were attributed to false-positive assay results, pseudodeficiency alleles (alleles that alter gene expression to produce low enzyme activity detected by assays but in the absence of clinical disease), and late-onset milder phenotypes [53]. All GD type-specific incidence estimates were from newborn screening programs. GD1 incidence was reported for Europe and North America only (0.45–22.9) and GD3 incidence for Asia-Pacific only (1.36), consistent with observed regional differences in the distribution of GD types, where GD3 is the most frequent disease type in the Asia-Pacific region. In a report published in December 2021 of data from 27 patients with GD in Thailand (seven centers) studied between 2010 and 2018, GD3 was the most common type (44.5%), followed by GD2 (40.7%) and GD1 (14.8%) [57]. When investigating average prevalence estimates there is potential for the inaccurate generalization of regional estimates, which can be distorted by estimates from specific ethnic groups and health-seeking populations. There is, therefore, a need for accurate and generalizable regional estimates applicable to mixed populations, together with a better understanding of incidence rates applicable to specific populations found within regions. Estimates of GD prevalence per 100,000 population varied considerably between regions, and there were few GD type-specific prevalence estimates that could be retrieved from publications—all three of the studies contributing GD type-specific prevalence estimates were from Europe [37,44,47]. Prevalence estimates per 100,000 population for any GD ranged from 0.02 to 139.0 from 17 studies; estimates were higher in North America (0.60–139.0) than other regions, including the Middle East (0.20–20.2, including Israel), Europe (0.02–1.1), and Latin America (0.15–0.32). The highest prevalence estimate was from a population of Ashkenazi Jewish descent in North America (139.0). The lowest prevalence estimates (0.02–0.08) were GD type-specific for GD2 and GD3, which might be expected given the poor prognosis of patients with neurologic forms of GD [58]. GD1 was the most prevalent GD type in Europe and North America, consistent with previous reporting [2,58]. The regional generalizability of prevalence estimates was considered adequate for North America, Europe, Latin America, and the Asia-Pacific region and intermediate for the Middle East (because no estimates were found for Egypt or Turkey, two of the four countries of the region with the largest population sizes). The heterogeneity of prevalence estimates within the same region could be attributed to the variable distribution of different ethnic groups, as exemplified by the range of prevalence estimates from the Middle East and North America [18,19]. When excluding GD type-specific estimates and data from Ashkenazi Jewish populations (where identified) and Israel, prevalence estimates ranged from 0.11 to 1.93, in line with the previous qualitative literature review estimate of 0.70–1.75 per 100,000 population derived from seven mixed population studies [2]. The global GD prevalence calculated from data pooled from four studies was 0.9 (95% CI 0.7–1.1) per 100,000 inhabitants [3]. Considering mixed population studies identified from our review, the lowest prevalence estimates found were for Latin America (0.15–0.32), followed by the Middle East (0.20–0.33, excluding estimates from Israel), Europe (0.11–1.1), and North America (0.60–1.93). Limitations The aim of this literature review—to provide a regional synthesis of recent GD incidence and prevalence estimates—took precedence over providing an all-encompassing summary of epidemiologic data available on GD. A targeted review was conducted for the period 2011 to 2020. Most incidence and prevalence estimates were identified from publications in the scientific literature indexed in MEDLINE and EMBASE using standard keyword terms; however, pragmatic searches of web-based resources and hand-searching of reference lists were included to widen the range of data sources included. Publication bias is considered less likely when reporting data from epidemiologic versus interventional clinical studies; however, this may still contribute to the lack of data available from English language scientific publications reporting on regions outside Europe and North America. It should be noted that a large proportion of GD prevalence estimates from Europe were derived from one publication (survey of The European Gaucher Alliance members) [22]; however, estimates from Israel and Spain in this study were in line with estimates for these countries from other studies. Estimates based on voluntary membership of national patient organizations may be less comprehensive in capturing all patients with GD than other health-system based surveys. Efforts to mitigate any study selection bias in the review included a quality control assessment of the screening and data extraction process by another assessor. The synthesis of GD incidence and prevalence estimates by region in this review highlighted significant data gaps. GD incidence was poorly documented overall, and GD type-specific estimates for incidence and prevalence were rare. Few estimates were available for GD2 and GD3. Specifically, limited epidemiologic data were available for the Asia-Pacific region, and none from India or Africa, although there are case reports of patients with GD from these countries [59,60,61,62]; a large proportion of the global population were not represented. The availability of epidemiologic data on GD is likely to reflect accessibility to healthcare, because the diagnosis of GD requires the use of techniques that are both invasive and resource intensive [62]. New technologies, such as the high-throughput digital microfluidic platform [63], may offer ways to provide inexpensive, minimally invasive disease-specific testing for LSDs in developing countries. International disease registries and treatment access programs could also improve data availability for these regions [61,64,65]. When considering the reliability and comparability of epidemiologic estimates from different studies included in this review, it should be noted that different screening platforms for GD were used across studies, few studies included data from newer genetic profiling technologies [17,57], and the types of assay and measures of accuracy were generally poorly documented. An additional caveat to the interpretation of data from newborn screening programs is that they can identify asymptomatic GD carriers, which may lead to overestimation of future disease burden in terms of number of patients experiencing clinical symptoms that will require healthcare intervention [19,53]. Recent studies—including those from biobanks investigating screening for diagnosed and undiagnosed patients with GD—have indicated that extrapolating disease frequency rates from average numbers may exaggerate the numbers with GD, particularly in populations that are stable and where mutations are at a low level [55,66]. For example, applying 1:30,000–100,000 prevalence estimates to Finland results in 60–180 more patients with GD than have currently been identified in the population, which overburdens the health service in its attempt to identify additional, non-existent patients [66]. The criteria for assessing the regional generalizability of estimates for this study have not been validated and were based on objective criteria only, such as geographical coverage of the region and countries with the largest population size. Consideration of the varying ethnic backgrounds for populations found in different regions may have been more informative, given the genetic profile of the disease. 5. Conclusions This literature review maps current regional and population-specific epidemiologic estimates for GD incidence and prevalence reported in the medical literature from the last 10 years. The generalizability of incidence and prevalence estimates to regional populations with available data was graded either as adequate or intermediate. A global overview of GD incidence and prevalence estimates identified important data gaps for specific regions such as Africa and countries with large populations, including India and China. Population estimates at specific time points can provide a useful benchmark from which to monitor future changes in GD incidence and prevalence and for tracking the emergence of new genetic variants associated with GD identified by genetic profiling. In the future, new diagnostic platforms—together with international disease registries and treatment access initiatives—may help to provide more accurate regional predictions for disease burden. |
doc8 | Genetic Research on Gaucher Disease Gaucher disease results from a mutation on the glucocerebrosidase (GCase) gene, causing low GCase enzyme activity. GCase enzyme breaks down glucocerebroside, a fatty chemical that builds up in the bodies of patients with Gaucher disease. New research on the genetics of Gaucher disease and the GCase gene are helping scientists understand how and why the disease affects patients differently. Key insights include: Number of mutations: Researchers have identified almost 300 mutations of the glucocerebrosidase (GCase) gene.[1] The variety of mutations may be part of the reason why Gaucher disease affects people so differently. Disease variability: Symptoms of Gaucher disease vary widely, even among identical twins with the same genetic mutation.[1] Researchers think that other processes in the body may determine disease onset, severity and progression. [2] For example, studies show that certain recycling processes in the cell can affect the buildup of abnormal proteins linked with Gaucher’s disease and associated conditions.[3] Parkinson disease link: Like Gaucher disease, some patients with Parkinson disease also have mutations in their GCase gene.[1] Mutations in this gene may increase the risk of both Parkinson and Lewy body dementia (LBD).[2] Learn more about Gaucher and Parkinson disease research. The Role of Protein Activity in Gaucher Disease Gaucher disease is one of the most common lysosomal storage disorders. Lysosomes are the body’s recycling centers, breaking down chemicals for reuse as well as waste products. A key role of lysosomes is to recycle proteins, which the body uses in many critical processes. One protein called alpha-synuclein works with the GCase enzyme and is essential for normal cell function. Studying this protein helps researchers better understand how the disease works, the first step in developing new therapies. Recent findings include: Balance of GCase enzyme and alpha-synuclein: The balance of GCase enzyme and alpha-synuclein may play a critical role in helping the body’s proteins work correctly. Too much alpha-synuclein may prevent the GCase enzyme from breaking down glucocerebroside.[3] Improper protein folding: Lab studies show a buildup of improperly folded alpha-synuclein in cases of low GCase enzyme levels. Proteins work like a lock and key, with a unique 3-D structure that lets them connect to drugs and other molecules in the body. When proteins are not folded correctly, it is like filling up a keyhole with glue. The abnormal folding of alpha-synuclein causes the proteins to clump together so they cannot do their job. Parkinson link: Abnormally folded alpha-synuclein may be an early trigger for Parkinson disease. It is often found in patients with Parkinson disease or LBD who also have a GCase gene mutation. The accumulation of abnormal proteins degrades neurons (brain cells) so they stop working correctly.[4] Learn more about Gaucher and Parkinson disease research. How Gaucher Disease Research May Lead to New Treatments Researchers are investigating new approaches to Gaucher disease treatment. These include: Reducing glucocerebroside: Scientists are screening large numbers of molecules (chemical compounds) to see which ones can lower glucocerebroside in the body. If they are successful, their results could lead to new drugs or add to current therapies.[3] Ideally, researchers will identify a drug that can cross the blood-brain barrier, which acts to protect the brain but also filters out medications. If they are successful, it could open up treatment options for Gaucher disease types 2 and 3. Using chaperone agents: Chaperone agents are drugs that keep proteins properly folded so they can work correctly and help GCase break down glucocerebroside.[3] Chaperone drugs also help drugs hit their target by escorting glucocerebroside to the lysosome where GCase can break it down. Treating Gaucher disease types 2 and 3: Lab studies in mice with symptoms of Gaucher disease types 2 and 3 show that decreasing the function of a protein called RIPK3 improved symptoms. However, more work needs to be done to find chemical compounds that will provide the same result in humans.[5] Gene Therapy, Bone Marrow Transplant and Stem Cell Transplant Gene therapy involves transplanting normal genes in place of defective ones. Some researchers are looking at gene therapy, but it has been a slow process. As researchers discover how gene therapy helps other genetic diseases, this work may provide new insights into Gaucher disease treatment. Some researchers are also investigating therapies like bone marrow and stem cell transplant. While these techniques are becoming safer, they are typically rejected for patients with Gaucher disease. The main reason is because the risks outweigh any potential benefits, with current therapies being more effective. Enzyme enhancement therapy (EET) offers a novel therapeutic strategy to increase the residual function of mutant proteins. EET employs small molecules as ‘pharmacological chaperones’ to rescue misfolded and/or unstable mutant enzymes or proteins that have residual function. EET, in conjunction with enzyme replacement therapy, also offers the possibility of treating neurodegenerative lysosomal disorders since these small therapeutic molecules may cross the blood-brain barrier. Patients with non-neuronopathic Gaucher disease (GD) and heterozygous GBA mutation carrier are at increased risk for Parkinson disease (PD). The risk for PD in these groups does not linearly increase with glucosylceramide (GC) accumulation or with acid glucocerebrosidase (GCase) activity. This observation suggests the possibility that extra-cellular GC actually has beneficial, anti-inflammatory properties; thus, supplementary oral GC administered to GBA carriers at risk for PD may slow inflammatory-driven secondary neuronal death. Ambroxol hydrochloride, a pharmacological chaperone, which reduces endoplasmic reticulum (ER) stress induced by accumulation of mutant misfolded GCase could serve as such an agent. This group proposed that the efficacy of this combined therapy should be evaluated in clinical trials. |
doc9 | "ABSTRACT Gaucher disease (GD) is a rare, genetic lysosomal disorder leading to lipid accumulation a(...TRUNCATED) |
doc10 | "Abstract Background Gaucher disease (GD) is one of the most prevalent lysosomal storage diseases an(...TRUNCATED) |
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Gaucher Disease QA
A long-form, multi-hop question answering dataset about Gaucher disease, a rare lysosomal storage disorder caused by mutations in the GBA1 gene.
Dataset Description
This dataset contains 25 expert-curated causal reasoning questions grounded in 20 biomedical articles covering the genetics, pathophysiology, clinical manifestations, and treatment of Gaucher disease. Each question requires synthesizing information from multiple source documents to produce a comprehensive answer, making it a challenging benchmark for multi-hop QA and biomedical causal inference.
Key Properties
- Domain: Biomedical / rare disease / genetics
- Question type: Long-form causal reasoning (not extractive)
- Multi-hop: Every question requires evidence from 2-4 source documents
- Total queries: 25
- Total documents: 20
- Total relevance judgments: 86
- Average documents per query: 3.4
Dataset Format (BEIR-style)
The dataset follows the BEIR format with three JSONL files:
queries.jsonl
{"id": "q1", "question": "How does a mutation in the GBA gene disrupt the catalytic activity of glucocerebrosidase?", "answer": "Mutations in the GBA gene can cause the enzyme to fold improperly..."}
corpus.jsonl
{"id": "doc1", "text": "Full article text..."}
qrels.jsonl
{"query_id": "q1", "doc_ids": ["doc1", "doc8", "doc15", "doc19"]}
Topics Covered
The questions span the full causal chain of Gaucher disease:
- Molecular basis: GBA1 mutations, enzyme misfolding, residual activity, genotype-phenotype correlations
- Cellular pathology: Glucocerebroside accumulation, Gaucher cell formation, lysosomal dysfunction
- Organ involvement: Splenomegaly, hepatomegaly, bone marrow infiltration, impaired hematopoiesis
- Neurological complications: Neuronopathic types 2/3, cognitive difficulties, Parkinson's disease link (alpha-synuclein/GCase vicious cycle)
- Metabolic effects: Hypermetabolism (REE 44% elevated), GM3-mediated insulin resistance, AKT pathway disruption
- Clinical management: ERT vs SRT (eliglustat/CYP2D6), splenectomy risks, biomarkers (chitotriosidase), imaging
- Emerging therapies: Gene therapy (AAV vectors, BBB crossing)
- Genetics: Autosomal recessive inheritance, genetic counseling
Usage
from datasets import load_dataset
dataset = load_dataset("jashparekh/gaucher-disease-qa")
Or load the JSONL files directly:
import json
queries = [json.loads(line) for line in open("queries.jsonl")]
corpus = [json.loads(line) for line in open("corpus.jsonl")]
qrels = [json.loads(line) for line in open("qrels.jsonl")]
Intended Use
- Benchmarking multi-hop question answering systems on biomedical text
- Evaluating causal reasoning over scientific/medical document collections
- Testing retrieval-augmented generation (RAG) pipelines on domain-specific content
- Evaluating knowledge graph-based QA systems for rare disease information
Source
All questions and gold answers were expert-curated and verified against the 20 source articles. The articles include clinical reviews, gene therapy research papers, patient-facing medical resources, and comprehensive disease overviews from sources such as GeneReviews, NORD, NIH, Mayo Clinic, and peer-reviewed journals.
Citation
This dataset was created as part of the SARG (Structure-Augmented Reasoning Generation) project. If you use this dataset, please cite:
@article{parekh2025structure,
title={Structure-Augmented Reasoning Generation},
author={Parekh, Jash Rajesh and Jiang, Pengcheng and Han, Jiawei},
journal={arXiv preprint arXiv:2506.08364},
year={2025}
}
License
MIT
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Size of downloaded dataset files:
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Number of rows:
70