Identification and expression of acid beta-glucosidase mutations causing severe type 1 and neurologic type 2 Gaucher disease in non-Jewish patients

Gaucher disease in North Macedonia: Unexpected prevalence of the N370S GBA1 allele with attenuated disease expression

The majority of Gaucher Disease (GD) cases result from pathologic mutations in the GBA1 gene. A rich mutational spectrum of about 500 identified variants has been recognized. The disease is characterized by phenotypic diversity. Data regarding the genotype-phenotype correlation are scanty and inconclusive. Here, we summarize the genetic and phenotypic “portraits” of 14 patients with GD type 1 in the Republic of North Macedonia, 4 of Macedonian and 10 of Albanian origin. Altogether, 6 variants were detected, compounding 6 different genotypes. All genotypes contained the N370S variant, which was detected with an overall prevalence of 60.7%. Other frequent variants included the 1263del55 deletion and the double mutant allele D409H;H255Q, each with a prevalence of 14.2%. We detected two rare mutations: W92* - a pathogenic nonsense mutation and D399N – a single nucleotide variant of uncertain pathogenicity. The most common genotypes were N370S/1263del55 and H255Q;D409H/N370S, both present in 4/14 patients, followed by N370S homozygosity (3/14). Splenomegaly was the most common clinical manifestation, identified in all patients. Hepatomegaly was less frequent and was present in 50% of cases. Thrombocytopenia was present in 9/14, while half of the patients had anemia. Bone pathology was demonstrated in 8 patients. Patients with different genotypes displayed a high degree of phenotypic heterogeneity, suggesting that the other allele determines the onset and severity of the disease in patients with the N370S mutation. Longer follow-up, bigger cohorts of patients and multicentric studies should be conducted to further define the association between the genotypic and phenotypic expression in GD.

A rare homozygous p.Arg87Trp variant of the GBA gene in Gaucher disease: A case report

Gaucher disease (GD) is a rare metabolic disorder due to pathogenic variants in the GBA gene. We report the first case of the rare p.Arg87Trp pathogenic variant (formerly known as R48W) of the GBA gene in the Tunisian population. A female Arab patient was assessed at the age of 26 due to abdominal distension, bone pain, and headache since she was 25. Physical examination revealed splenomegaly, rib deformation, lumbar scoliosis, and upper limb tremor. Bone marrow was infiltrated by Gaucher cells. The patient was homozygous for the rare p.Arg87Trp variant which is known to be associated with a mild phenotype. This report highlights the necessity of screening the Tunisian population for this rare variant.

Gaucher disease is the most common inherited lysosomal storage disorder. It is a multisystem condition resulting from glucocerebrosidase deficiency, with high inter‐ and intrafamilial phenotypic variability. Gaucher disease patients can be eligible for enzymatic replacement therapy. Therefore, it should be suspected in adults presenting with unexplained splenomegaly and skeletal deformities.

Association Between Glucocerebrosidase Mutations and Parkinson's Disease in Ireland

Multiple studies implicate heterozygous GBA mutations as a major genetic risk factor for Parkinson's disease (PD); however, the frequency of mutations has never been examined in PD patients from the Irish population. We prospectively recruited 314 unrelated Irish PD patients (UK Brain Bank Criteria) and 96 Irish healthy controls (without any signs or family history of parkinsonism) attending. The Dublin Neurological Institute (DNI). Complete exon GBA Sanger sequencing analysis with flanking intronic regions was performed. The GBA carrier frequency was 8.3% in PD and 3.1% in controls. We identified a number of potentially pathogenic mutations including a p.G195E substitution and a p.G377C variant, previously described in a case study of Gaucher's disease in Ireland. On genotype–phenotype assessment hallucinations, dyskinesia, and dystonia were more prevalent in GBA-PD. The genetic etiology of PD in Ireland differs from the continental Europe as seen with the lower LRRK2 and higher than in most European countries GBA mutation frequency. Determining genetic risk factors in different ethnicities will be critical for future personalized therapeutic approach.

Stabilization of Glucocerebrosidase by Active Site Occupancy

Glucocerebrosidase (GBA) is a lysosomal β-glucosidase that degrades glucosylceramide. Its deficiency results in Gaucher disease (GD). We examined the effects of active site occupancy of GBA on its structural stability. For this, we made use of cyclophellitol-derived activity-based probes (ABPs) that bind irreversibly to the catalytic nucleophile (E340), and for comparison, we used the potent reversible inhibitor isofagomine. We demonstrate that cyclophellitol ABPs improve the stability of GBA in vitro, as revealed by thermodynamic measurements (T_m increase by 21 °C), and introduce resistance to tryptic digestion. The stabilizing effect of cell-permeable cyclophellitol ABPs is also observed in intact cultured cells containing wild-type GBA, N370S GBA (labile in lysosomes), and L444P GBA (exhibits impaired ER folding): all show marked increases in lysosomal forms of GBA molecules upon exposure to ABPs. The same stabilization effect is observed for endogenous GBA in the liver of wild-type mice injected with cyclophellitol ABPs. Stabilization effects similar to those observed with ABPs were also noted at high concentrations of the reversible inhibitor isofagomine. In conclusion, we provide evidence that the increase in cellular levels of GBA by ABPs and by the reversible inhibitor is in part caused by their ability to stabilize GBA folding, which increases the resistance of GBA against breakdown by lysosomal proteases. These effects are more pronounced in the case of the amphiphilic ABPs, presumably due to their high lipophilic potential, which may promote further structural compactness of GBA through hydrophobic interactions. Our study provides further rationale for the design of chaperones for GBA to ameliorate Gaucher disease.

Participation of asparagine 370 and glutamine 235 in the catalysis by acid beta-glucosidase: the enzyme deficient in Gaucher disease

The hydrolysis of glucosylceramide by acid beta-glucosidase proceeds via a two-step, double displacement mechanism that includes cleavage of the O-beta-glucosidic bond, enzyme-glucosylation and, then, enzyme-deglucosylation. Two residues that may impact this cycle are N370 and E235. The N370S mutant enzyme is very common in Gaucher disease type 1 patients. Homology and crystal data predictions suggested that E235 is the acid/base catalyst in the hydrolytic reaction. Here, the roles of N370 and E235 in hydrolysis were explored using mutant proteins with selected amino acid substitutions. Heterologously expressed enzymes were characterized using inhibitors, activators, and alternative substrates to gain insight into the effects on the glucosylation (single turnover) and deglucosylation (transglucosylation) steps in catalysis. Specific substitutions at N370 selectively altered only the glucosylation step whereas N370S altered this and the deglucosylation steps. To provide functional data to support E235 as the acid/base catalyst, progress curves with poor substrates with more acidic leaving groups were used in the presence and absence of azide as an exogenous nucleophile. The restoration of E235G activity to nearly wild-type levels was achieved using azide with 2,4-dinitrophenyl-beta-glucoside as substrate. The loss of the acidic arm of the pH optimum activity curve of E235G provided additional functional support for E235 as the acid/base in catalysis. This study provides insight into the function of these residues in acid beta-glucosidase active site function.

Treatment perspectives for the lysosomal storage diseases

BACKGROUND

The therapy of the lysosomal storage diseases (LSDs) was developed by supplying adequate amounts of the needed enzyme to affected individuals. This approach in Gaucher disease provided a prototype for the basic and clinical sciences, and the economic foundation for other ultra-orphan diseases.

OBJECTIVE

Using the success of enzyme therapy for Gaucher disease, the challenges are highlighted for alternative bioproduction systems, and substrate reduction and molecular chaperone approaches for treatment of Gaucher disease and other ultra-orphan diseases.

METHODS

Literature review provided insight into the current status of enzyme therapies for LSDs, the proposed mechanisms of alternative approaches to therapy, and the obstacles in a competitive marketplace for treatment of ultra-rare diseases.

RESULTS/CONCLUSIONS

These developments are placed in the contexts of finding rare patients with LSDs, their marked phenotypic spectrum, potential markets, and new orphan drug costs. The confluence of these challenges has led to a competitive environment with the potential for multiple, alternative, expensive treatments for orphan diseases.

An evolutionary and structure-based docking model for glucocerebrosidase-saposin C and glucocerebrosidase-substrate interactions - relevance for Gaucher disease

Gaucher disease, the most prevalent lysosomal storage disorder, is principally caused by malfunction of the lysosomal enzyme glucocerebrosidase (GBA), a 497-amino acid membrane glycoprotein that catalyzes the hydrolysis of glucosylceramide to ceramide and glucose in the presence of an essential 84-residue activator peptide named saposin C (SapC). Knowledge of the GBA structure, a typical (beta/alpha)(8) TIM barrel, explains the effect of few mutations, directly affecting or located near the catalytic site. To identify new regions crucial for proper GBA functionality, we analyzed the interactions of the enzyme with a second (substrate) and a third (cofactor) partner. We build 3D docking models of the GBA-SapC and the GBA-ceramide interactions, by means of methodologies that integrate both evolutive and structural information. The GBA-SapC docking model confirm the implication of three spatially closed regions of the GBA surface (TIM barrel-helix 6 and helix 7, and the Ig-like domain) in binding the SapC molecule. This model provides new basis to understand the pathogenicity of several mutations, such as the prevalent Leu444Pro, and the additive effect of Glu326Lys in the double mutant Glu326Lys-Leu444Pro. Overall, 39 positions in which amino acid changes are known to cause Gaucher disease were localized in the GBA regions identified in this work. Our model is discussed in relation to the phenotype (pathogenic effect) of these mutations, as well as to the enzymatic activity of the recombinant proteins when available. Both data fully correlates with the proposed model, which will provide a new tool to better understand Gaucher disease and to design new therapy strategies.

Gaucher disease: different clinical manifestations associated with a rare mutation (R48W) in a Lebanese family

Gaucher disease (GD) is the most frequently encountered lysosomal storage disease, caused by autosomal recessive inborn defects in the glucocerebrosidase gene (GBA) at 1q21. The disease is most common in the Ashkenazi Jewish population. GD can present with a vast phenotypic heterogeneity, which can be predicted to some extent from the underlying mutation. In this report, we describe a Lebanese Arab family with multigenerational incidence of GD caused by a heterozygous genotype of a rare mutation, R48W, and a common one, L444P. Our patients' clinical course is described. We also review the English literature for patients with this rare mutation.

Chemical chaperones and permissive temperatures alter localization of Gaucher disease associated glucocerebrosidase variants

Point mutations in the lysosomal hydrolase, glucocerebrosidase (GC), can cause Gaucher disease, a common lysosomal storage disease. Several clinically important GC mutations impede folding in the endoplasmic reticulum (ER) and target these enzymes for ER-associated degradation (ERAD). The removal of these misfolded proteins decreases the lysosomal concentration of GC, which results in glucosylceramide accumulation. The most common GC variant, N370S, and other clinically relevant variants, G202R and L444P, exhibit different cellular localization patterns in patient-derived fibroblasts. We show that these distributions can be altered by manipulation of the ER folding environment, either by chemical chaperones or by temperature shifts. N370S, L444P, and G202R GC are destabilized in the neutral pH environment of the ER, rendering them prone to ERAD. Fibroblasts harboring the G202R and L444P GC mutations grown at 30 degrees C localize the mutant proteins to the lysosome, and this increases total GC activity. Both of these temperature-sensitive mutants appear to be stable at 37 degrees C once they are trafficked to the low pH environment of the lysosome. Chemical chaperones correct the ER instability and significant ER retention of G202R GC. N370S is also destabilized under ER simulating conditions, a deficiency that is corrected by chemical chaperone binding. These data clearly show manipulating the ER environment with chemical chaperones increases the lysosomal concentration of partially active GC variants and suggest that small molecules could be used to treat Gaucher disease.

Analyses of variant acid beta-glucosidases: effects of Gaucher disease mutations

Acid beta-glucosidase (GCase) is a 497-amino acid, membrane-associated lysosomal exo-beta-glucosidase whose defective activity leads to the Gaucher disease phenotypes. To move toward a structure/function map for disease mutations, 52 selected single amino acid substitutions were introduced into GCase, expressed in an insect cell system, purified, and characterized for basic kinetic, stability, and activator response properties. The variant GCases from Gaucher disease patients and selected variant GCases from the mouse had decreased relative k(cat) and differential effects on active site binding and/or attachment of mechanism-based covalent (conduritol B epoxide) or reversible (deoxynojirimycin derivatives) inhibitors. A defect in negatively charged phospholipid activation was present in the majority of variant GCases but was increased in two, N370S and V394L. Deficits in saposin C enhancement of k(cat) were present in variant GCases involving residues 48-122, whereas approximately 2-fold increases were obtained with the L264I GCase. About 50% of variant GCases each had wild-type or increased sensitivity to in vitro cathepsin D digestion. Mapping of these properties onto the crystal structures of GCase indicated wide dispersion of functional properties that can affect catalytic function and stability. Site-directed mutagenesis of cysteine residues showed that the disulfide bonds, Cys(4)-Cys(16) and Cys(18)-Cys(23), and a free Cys(342) were essential for activity; the free Cys(126) and Cys(248) were not. Relative k(cat) was highly sensitive to a His substitution at Arg(496) but not at Arg(495). These studies and high phylogenetic conservation indicate localized and general structural effects of Gaucher disease mutations that were not obvious from the nature of the amino acid substitution, including those predicted to be nondisruptive (e.g. Val --> Leu). These results provide initial studies for the engineering of variant GCases and, potentially, molecular chaperones for therapeutic use.

Gaucher Disease-Associated Glucocerebrosidases Show Mutation-Dependent Chemical Chaperoning Profiles

Gaucher disease is a lysosomal storage disorder caused by deficient glucocerebrosidase activity. We have previously shown that the cellular activity of the most common Gaucher disease-associated glucocerebrosidase variant, N370S, is increased when patient-derived cells are cultured with the chemical chaperone N-nonyl-deoxynojirimycin. Chemical chaperones stabilize proteins against misfolding, enabling their trafficking from the endoplasmic reticulum. Herein, the generality of this therapeutic strategy is evaluated with other glucocerebrosidase variants and with additional candidate chemical chaperones. Improved chemical chaperones are identified for N370S glucocerebrosidase. Moreover, we demonstrate that G202R, a glucocerebrosidase variant that is known to be retained in the endoplasmic reticulum, is also amenable to chemical chaperoning. The L444P variant is not chaperoned by any of the active site-directed molecules tested, likely because this mutation destabilizes a domain distinct from the catalytic domain.

Impaired trafficking of mutants of lysosomal glucocerebrosidase in Gaucher's disease

Gaucher's disease is the most inherited lysosomal storage disorder. Except for a few cases, the broad phenotypic heterogeneity of Gaucher's disease can be neither predicted from defined mutations nor from differences in residual enzyme activity. Here, we analyse the intracellular trafficking of glucocerebrosidase as an underlying mechanism for the expression of the clinical phenotype. Biosynthetic labeling studies combined with immunofluorescence analyses with fibroblasts from patients with the defined mutations N370S, L444P, D409H and G202R unequivocally demonstrate a retarded transport of glucocerebrosidase carrying the mutation N370S and a transport block in the ER of the enzyme with the mutations G202R, L444P and D409H. We asked whether cellular components in the patients' fibroblasts other than glucocerebrosidase are implicated in the onset of the disease. For this, mutant cDNA's corresponding to the phenotypes N370S, G202R and L444P were expressed in the mouse fibroblasts NIH3T3. Essentially similar biochemical and cellular features were revealed as compared to the patients' fibroblasts strongly suggesting that these mutations are exclusively responsible for the characterized phenotypes. Interestingly, the immunoglobulin binding protein (BiP) binds wild type and the mutant N370S but not the G202R and L444P variants suggesting a discriminatory role played by this chaperone associated with the severity of the disease.

Nitric oxide regulates synthesis of gene products involved in keratinocyte differentiation and ceramide metabolism

During terminal differentiation of keratinocytes the expression of various proteins, which are required for the formation of the epidermal water barrier in the skin of land dwelling animals, is upregulated. Using a cell culture model for the differentiation of human keratinocytes and real-time PCR, we quantified the mRNA levels of several proteins involved in differentiation and ceramide metabolism. A calcium shift (1.1 mM CaCl2, 10 microM linoleic acid) for 8 days triggered an increase in mRNA levels of keratin 10 (75-fold), profilaggrin (55-fold), glucosylceramide synthase (40-fold), beta-glucocerebrosidase (30-fold), prosaposin (15-fold), acid sphingomyelinase (5-fold), and serine palmitoyltransferase (SPTLC2, 4-fold). However, mRNA levels of keratin 14 and acid ceramidase did not change significantly. On the other hand nitric oxide added at concentrations lower than 0.25mM stimulates proliferation of keratinocytes (Krischel et al., J. Invest. Dermatol. 111, 286-291, 1998). Accordingly, the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 0.2 mM) had no effect on the morphology of cultured keratinocytes, whereas in cultured human fibroblasts apoptosis was induced. The expression patterns obtained suggest that keratinocytes remain in a basal proliferative state, with a 3-fold increase in keratin 14 expression, a marked decrease in mRNA levels of differentiation markers and of most ceramide-metabolizing enzymes to negligible levels. The inhibitor of the NO synthase, N(G)-nitro-L-arginine-methyl ester (L-NAME, 10 mM), induced a transient increase in ceramide formation, followed by apoptosis in keratinocytes but not in fibroblasts. Both, SNAP and L-NAME, decreased the mRNA levels of all proteins involved in ceramide metabolism.

Novel mutation, L371V, causing multigenerational Gaucher disease in a Lebanese family

We have identified six individuals over three generations within a Lebanese-Arab family affected with Gaucher disease. This family is unusual and informative because affected members are homozygous for a previously unidentified mutation, L371V. Clinical symptoms begin in early childhood and progress to moderately severe involvement by young adulthood. There is significant anemia, thrombocytopenia, and bony involvement, but no mental deterioration. The phenotype is more severe than the phenotype observed in the common mutation associated with type 1 Gaucher disease, N370S. It is unknown whether L371V is a private mutation limited to this family, or will prove to be a common mutation within the Lebanese population.

Gaucher's disease: identification of novel mutant alleles and genotype-phenotype relationships

A sequencing protocol for the acid beta-glucosidase (GCase) gene (GBA) was developed using a long-range PCR template. This protocol has an advantage of greater DNA yields over similar strategies. Seven Gaucher's disease patients had four novel and five other rare alleles. A non-pseudogene in-frame deletion (g.2600-2602delTAC) and a new complex mutation (null allele) were identified in Gaucher's disease type 1, i.e. the g.2600-2602delTAC deletion is associated with the non-neuronopathic variant. An F251L allele was found in a baby with the collodion skin phenotype. Three mutant alleles were identified in a single primary family with type 3. The patients' father at 45 years is healthy and is heteroallelic for the G202R and E326K alleles. Family studies indicated that E326K is in trans to G202R and L444P, and that isolated E326K is non-pathogenic in this family. A rare mutation R257Q was identified in a type 2 patient, providing an association with neuronopathic disease. A genotype L444P/L444P was noted in a 22-year-old non-neuronopathic patient. Complete gene sequencing showed a new complex allele consisting of L444P and g.7741T > C in the 3' UTR. Three additional complex alleles also involved the 3' UTR. Complete gene characterization in Gaucher's disease should allow greater insights into the correlation of specific alleles with phenotype.

Transient expression of wild-type and mutant glucocerebrosidases in hybrid vaccinia expression system

Gaucher disease, the most prevalent lysosomal storage disease, is characterised by a significant phenotypic variation caused by more than 150 mutations. In order to verify pathogenicity of mutations found in the Czech Gaucher population, the vaccinia expression system was used. The wild-type human beta-glucocerebrosidase cDNA and cDNAs carrying the mutations 72delC, 1326insT, 1263del55, S196P, N370S, L444P, G202E, D409H, T369M, L444P+V460V, and D409H+T369M were expressed in Gaucher fibroblast cell line (L444P/S107L), BSC40, and HeLa G cells. The enzymatic activity and immunological reactivity were analysed. Only beta-glucocerebrosidase-deficient fibroblasts were suitable for expression using plasmid transfection. The expressed beta-glucosidase activity of mutant glucocerebrosidases was in good correlation with the presumed severity of the mutations.

Mutation analysis of the acid beta-glucosidase gene in a patient with type 3 Gaucher disease and neutralizing antibody to alglucerase

The beneficial effects of macrophage-targeted glucocerebrosidase (alglucerase, Ceredase) in patients with Gaucher disease are well established. A minority of recipients develop transient non-neutralizing antibodies to the exogenous enzyme. A 7-year-old patient with type 3 Gaucher disease, whose clinical course began to deteriorate while receiving alglucerase developed a progressively increasing titer of IgG antibody, that blocked the catalytic activity of alglucerase. We investigated the acid beta-glucosidase genotype in this patient. Direct sequencing of both cDNA and genomic PCR products was used to characterize the mutations underlying acid beta-glucosidase deficiency. The patient was shown to be a compound heterozygote for a previously reported missense mutation (G377S), and a novel single nucleotide deletion (g5255delT). The transcript originating from the latter allele was undetectable in RT-PCR experiments. We report the first characterization of a GBA genotype associated with the development of neutralizing antibody to alglucerase, in a patient affected with type 3 Gaucher disease. Our results may help to shed light on the mechanisms underlying this phenomenon which, in the rare instances where it occurs, hampers the efficacy of enzyme replacement therapy.

Glucocerebrosidase mutations among African-American patients with type 1 Gaucher disease

While the inherited deficiency of the enzyme glucocerebrosidase (Gaucher disease) is panethnic in its distribution, there have not been studies of the mutations encountered in specific ethnic groups in the United States, other than those on Ashkenazi Jews. We present the clinical descriptions and genotypes of seven patients of African-American ancestry with type 1 Gaucher disease, and summarize the published literature regarding the genotypes encountered in this population. All seven of the patients had moderate-to-severe manifestations of the disease, and all developed symptoms by adolescence. Genotypic analyses revealed that no two probands shared the same genotype. The common mutations N370S, c.84-85insG, IVS2+1 G-->A, and R463C were not seen. Mutation L444P was present on one allele in each of the patients; but the same mutation was encountered as a single point mutation in three of the patients, and as part of a recombinant allele in four of the patients. Southern blot analyses revealed a glucocerebrosidase fusion allele in one patient, and a duplication resulting from recombination in the region downstream from the glucocerebrosidase gene in three of the patients. Five different point mutations (A90T, R48W, N117D, R170C, and V352L), one deletion mutation (c.222-224 delTAC), and one insertion mutation (c.153-154 insTACAGC) were encountered. Our results demonstrate that there is significant genotypic heterogeneity among African-American patients with type 1 Gaucher disease, and that recombinations in the glucocerebrosidase gene locus are particularly common in this patient group. Published 2001 Wiley-Liss, Inc.

Carrier screening for Gaucher disease in couples of mixed ethnicity

With the advent of mutational analysis for Gaucher disease, carrier screening has been incorporated into many Jewish genetic disease screening programs. Frequencies and mutations for Gaucher disease in non-Jewish populations are less well established and the detection rate of carriers are lower. Testing is problematic for resolving residual risk in a couple of mixed ethnicity. We report the testing choices made by 20 consecutive couples of mixed ethnicity where the Ashkenazi Jewish partner was identified to be a Gaucher disease gene carrier. Carrier studies of the non-Jewish partner were elected as follows: DNA studies alone, 5 (25%); enzymatic assay, 2 (10%); both, 6 (30%); no carrier studies, 7 (35%). Of the 7 couples not electing carrier studies, one was not in a pregnancy and 6 elected prenatal diagnosis in lieu of parental testing by enzymatic analysis of amniocytes. One couple elected parental carrier studies as well as prenatal diagnosis. All couples electing prenatal Gaucher determination had amniocentesis for other indications as well (4, advanced maternal age; 4, parental anxiety). We conclude that Gaucher screening is feasible for couples of mixed ethnicity if appropriate counseling and testing are offered.

Molecular analysis and clinical findings in the Spanish Gaucher disease population: putative haplotype of the N370S ancestral chromosome

Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the lysosomal beta-glucocerebrosidase (GBA) gene. As the disease is particularly prevalent among Ashkenazi Jews, most studies have been carried out on this ethnic group. In the current study, we present a mutation analysis of the GBA gene in Spanish patients together with the clinical findings. We conducted a systematic analysis in 53 unrelated GD patients. The GBA gene was initially scanned for nine previously described mutations by ASO hybridization or restriction analysis after PCR amplification. The remaining unidentified alleles were screened by nonisotopic PCR-SSCP analysis and sequenced. This approach allowed the identification of 101 of 106 GD alleles (95.3%) involving 24 different mutations, 11 of which are described for the first time: G113E (455G-->A), T134P (517A-->C), G389E (1283G-->A), P391L (1289C-->T), N392I (1292A-->T), Y412H (1351T-->G), W(-4)X (108G-->A), Q169X (662C-->T), R257X (886C-->T), 500insT, and IVS5+1G-->T. Most mutations are present in one or few GD chromosomes. However, two mutations, N370S (1226A-->G) and L444P (1448T-->C), are very frequent and account for 66.1% of the total number of alleles. Linkage disequilibrium was detected between these two mutations and an intragenic polymorphism, indicating that expansion of founder alleles occurred in both cases. Analysis of several microsatellite markers close to the GBA gene allowed us to establish the putative haplotype of the ancestral N370S chromosome.

Analysis and classification of 304 mutant alleles in patients with type 1 and type 3 Gaucher disease

Gaucher disease results from the inherited deficiency of the enzyme glucocerebrosidase (EC 3.2.1.45). Although >100 mutations in the gene for human glucocerebrosidase have been described, most genotype-phenotype studies have focused upon screening for a few common mutations. In this study, we used several approaches-including direct sequencing, Southern blotting, long-template PCR, restriction digestions, and the amplification refraction mutation system (ARMS)-to genotype 128 patients with type 1 Gaucher disease (64 of Ashkenazi Jewish ancestry and 64 of non-Jewish extraction) and 24 patients with type 3 Gaucher disease. More than 97% of the mutant alleles were identified. Fourteen novel mutations (A90T, N117D, T134I, Y135X, R170C, W184R, A190T, Y304X, A341T, D399Y, c.153-154insTACAGC, c.203-204insC, c.222-224delTAC, and c.1122-1123insTG) and many rare mutations were detected. Recombinant alleles were found in 19% of the patients. Although 93% of the mutant alleles in our Ashkenazi Jewish type 1 patients were N370S, c.84-85insG, IVS2+1G-->A or L444P, these four mutations accounted for only 49% of mutant alleles in the non-Jewish type 1 patients. Genotype-phenotype correlations were attempted. Homozygosity or heterozygosity for N370S resulted in type 1 Gaucher disease, whereas homozygosity for L444P was associated with type 3. Genotype L444P/recombinant allele resulted in type 2 Gaucher disease, and homozygosity for a recombinant allele was associated with perinatal lethal disease. The phenotypic consequences of other mutations, particularly R463C, were more inconsistent. Our results demonstrate a high rate of mutation detection, a large number of novel and rare mutations, and an accurate assessment of the prevalence of recombinant alleles. Although some genotype-phenotype correlations do exist, other genetic and environmental factors must also contribute to the phenotypes encountered, and we caution against relying solely upon genotype for prognostic or therapeutic judgements.

Glucocerebrosidase gene mutations in patients with type 2 Gaucher disease

Gaucher disease, the most common lysosomal storage disorder, results from the inherited deficiency of the enzyme glucocerebrosidase. Three clinical types are recognized: type 1, non-neuronopathic; type 2, acute neuronopathic; and type 3, subacute neuronopathic. Type 2 Gaucher disease, the rarest type, is progressive and fatal. We have performed molecular analyses of a cohort of 31 patients with type 2 Gaucher disease. The cases studied included fetuses presenting prenatally with hydrops fetalis, infants with the collodion baby phenotype, and infants diagnosed after several months of life. All 62 mutant glucocerebrosidase (GBA) alleles were identified. Thirty-three different mutant alleles were found, including point mutations, splice junction mutations, deletions, fusion alleles and recombinant alleles. Eleven novel mutations were identified in these patients: R131L, H255Q, R285H, S196P, H311R, c.330delA, V398F, F259L, c.533delC, Y304C and A190E. Mutation L444P was found on 25 patient alleles. Southern blots and direct sequencing demonstrated that mutation L444P occurred alone on 9 alleles, with E326K on one allele and as part of a recombinant allele on 15 alleles. There were no homozygotes for point mutation L444P. The recombinant alleles that included L444P resulted from either reciprocal recombination or gene conversion with the nearby glucocerebrosidase pseudogene, and seven different sites of recombination were identified. Homozygosity for a recombinant allele was associated with early lethality. We have also summarized the literature describing mutations associated with type 2 disease, and list 50 different mutations. This report constitutes the most comprehensive molecular study to date of type 2 Gaucher disease, and it demonstrates that there is significant phenotypic and genotypic heterogeneity among patients with type 2 Gaucher disease. Hum Mutat 15:181-188, 2000. Published 2000 Wiley-Liss, Inc.

Intracellular transport of acid beta-glucosidase and lysosome-associated membrane proteins is affected in Gaucher's disease (G202R mutation)

Gaucher's disease (GD) is caused by an inherited deficiency of acid beta-glucosidase with storage of glucosylceramides in the lysosomes of macrophages. This study identifies a G202R mutation in the acid beta-glucosidase gene in an infant with severe neuronopathic (type 2) GD and only slightly reduced acid beta-glucosidase activity. Western blot analysis, pulse chase experiments, and the thin frozen section immunogold method were used to analyse the implications of this mutation on the pathogenesis, clinical heterogeneity and diagnostic evaluation of GD. The results show that acid beta-glucosidase persists in the patient's fibroblasts as a mannose-rich polypeptide in the endoplasmic reticulum and is not transported to the lysosomes. By contrast, high expression of the lysosome-associated membrane proteins LAMP-1 and LAMP-2, saposin C, and cathepsin D was observed in the patient's lysosomes. Immunogold labelling of the integral membrane proteins LAMP-1 and LAMP-2 increases significantly at the cell surface of Kupffer cells and fibroblasts as well as at the apical membrane of hepatocytes. In addition, LAMP-1 and LAMP-2 associate with the bilayer of stored glucosylceramide. It is concluded that defective intracellular transport of mutant acid beta-glucosidase from the endoplasmic reticulum to lysosomes leads to a more severe clinical phenotype than the residual enzyme activity may indicate. Furthermore, the detection of LAMP in the tubular bundles of undigested glucosylceramides, as well as their increased concentration at the surfaces of the affected cells, suggests that these proteins play a role in the storage or removal of substrate in GD. Intracellular targeting of acid beta-glucosidase and LAMP contributes to the broad phenotypic heterogeneity of GD.

Non-pseudogene-derived complex acid beta-glucosidase mutations causing mild type 1 and severe type 2 gaucher disease

Gaucher disease is an autosomal recessive inborn error of glycosphingolipid metabolism caused by the deficient activity of the lysosomal hydrolase, acid beta-glucosidase. Three phenotypically distinct subtypes result from different acid beta-glucosidase mutations encoding enzymes with absent or low activity. A severe neonatal type 2 variant who presented with collodion skin, ichthyosis, and a rapid neurodegenerative course had two novel acid beta-glucosidase alleles: a complex, maternally derived allele, E326K+L444P, and a paternally inherited nonsense mutation, E233X. Because the only other non-pseudogene-derived complex allele, D140H+E326K, also had the E326K lesion and was reported in a mild type 1 patient with a D140H+E326K/K157Q genotype, these complex alleles and their individual mutations were expressed and characterized. Because the E233X mutation expressed no activity and the K157Q allele had approximately 1% normal specific activity based on cross-reacting immunologic material (CRIM SA) in the baculovirus system, the residual activity in both patients was primarily from their complex alleles. In the type 1 patient, the D140H+E326K allele was neuroprotective, encoding an enzyme with a catalytic efficiency similar to that of the N370S enzyme. In contrast, the E326K+L444P allele did not have sufficient activity to protect against the neurologic manifestations and, in combination with the inactive E233X lesion, resulted in the severe neonatal type 2 variant. Thus, characterization of these novel genotypes with non-pseudogene-derived complex mutations provided the pathogenic basis for their diverse phenotypes.

Clinical and molecular characteristics of Japanese Gaucher disease

Clinical signs and symptoms of Gaucher disease are more severe in Japanese than in Jewish and other non-Japanese patients. A higher percentage of bone crises and splenectomy was demonstrated by Japanese patients, and there were five fatalities among patients with type 1 Gaucher disease. Additionally, neonatal Gaucher disease, clinically characterized by hydrops foetalis, was observed. Japanese patients with type 2 and type 3 disease also demonstrate clinical heterogeneity. About 100 alleles of patients with Japanese Gaucher disease were examined for genotype determination with the PCR and SSCP methods. About 18 different mutations, including several novel mutations in Japanese patients, were identified. The most common mutations in Japanese patients were 1448C(L444P), accounting for 41 (41%) of alleles. The second most prevalent mutation was 754A(F2131), accounting for 14 (14%) of alleles. Other alleles identified included the 1324C, IVS2 and other mutations. Unidentified alleles comprised 16% of the total number of alleles studied. To date, neither the 1226G (N370S) nor the 84GG mutation has been identified in the Japanese population, although these mutations account for about 70% and 10% of the mutations in Jewish and other non-Japanese populations, respectively. The phenotype-genotype correlation in Japanese patients is more complex compared with that of the Jewish population. In Japanese patients, the 1448C mutation, in either heteroallelic or homoallelic forms, exhibits both neurological and non-neurological phenotypes. Japanese patients with the 754A mutation also exhibit both neuronopathic and non-neuronopathic disease. On the other hand, patients with the D409H mutation show only type 3 neurological disease, and those with the 1447-1466 del 20 ins TG mutation have the severe, neonatal neurological form of Gaucher disease. The 1503T allele was present only in patients with type 1 non-neurological disease. However, since this correlation was observed only in young patients, we do not as yet know the final phenotypic outcome of this mutation. Probably, Japanese patients with Gaucher disease have few mutations that exhibit non-neurological signs and symptoms.

Exhaustive screening of the acid beta-glucosidase gene, by fluorescence-assisted mismatch analysis using universal primers: mutation profile and genotype/phenotype correlations in Gaucher disease

Gaucher disease (GD) is one of the most prevalent lysosomal storage disorders and one of the rare genetic diseases now accessible to therapy. Outside the Ashkenazi Jewish community, a high molecular diversity is observed, leaving approximately 30% of alleles undetected. Nevertheless, very few exhaustive methods have been developed for extensive gene screening of a large series of patients. Our approach for a complete search of mutations was the association of fluorescent chemical cleavage of mismatches with a universal strand-specific labeling system. The glucocerebrosidase (GBA) gene was scanned by use of a set of six amplicons, comprising 11 exons, all exon/intron boundaries, and the promoter region. By use of this screening strategy, the difficulties due to the existence of a highly homologous pseudogene were easily overcome, and both GD mutant alleles were identified in all 25 patients studied, thus attesting to a sensitivity that approaches 100%. A total of 18 different mutations and a new glucocerebrosidase haplotype were detected. The mutational spectrum included eight novel acid beta-glucosidase mutations: IVS2 G(+1)-->T, I119T, R170P, N188K, S237P, K303I, L324P, and A446P. These data further indicate the genetic heterogeneity of the lesions causing GD. Established genotype/phenotype correlations generally were confirmed, but notable disparities were disclosed in several cases, thus underlining the limitation in the prognostic value of genotyping. The observed influence of multifactorial control on this monogenic disease is discussed.

Genotypic heterogeneity and phenotypic variation among patients with type 2 Gaucher's disease

Gaucher's disease, the inherited deficiency of glucocerebrosidase, manifests with vast phenotypic variation. Even among patients with type 2 (acute neuronopathic) Gaucher's disease, there is a spectrum of clinical presentations. DNA samples from 14 patients with type 2 Gaucher's disease with a course ranging from intrauterine death at 22 wk of gestation to survival until age 30 mo were studied. L444P was the only common mutation identified, found in 15 patients' alleles. Sequencing of genomic DNA amplified by long template PCR revealed that mutation L444P occurred as a single point mutation in seven mutant alleles and as part of a recombinant allele in eight mutant alleles. Two patients had a deletion of 55 bp in exon 9; in one patient the deletion was part of a recombinant allele, and in a second the deletion occurred alone. Direct sequencing identified R120W on one allele, P415R on another, and one fetus was homoallelic for a deletion of a C nucleotide at codon 139 in exon 5. Eight of the mutant alleles remain unidentified. Northern blots revealed an appropriately sized mRNA in all except one of the patients studied. Of the 14 type 2 Gaucher patients, three had hydrops fetalis and died in utero or at birth, five had congenital ichthyosis, and seven survived 5 mo or more. Patients who died in the neonatal period had decreased protein detected by Western blot, regardless of genotype observed. These studies demonstrate that genotypic heterogeneity exists in patients with type 2 Gaucher's disease, even among infants with the most severe phenotypes.