Gaucher disease: gene frequencies in the Ashkenazi Jewish population.

DNA from over 2,000 Ashkenazi Jewish subjects has been examined for the four most common Jewish Gaucher disease mutations, which collectively account for about 96% of the disease-producing alleles in Jewish patients. This population survey has made possible the estimation of gene frequencies for these alleles. Eighty-seven of 1,528 individuals were heterozygous for the 1226G (N370S) mutation, and four presumably well persons were homozygous for this mutation. The gene frequency for the 1226G allele was calculated to be .0311, and when these data were pooled with those obtained previously from another 593 Jewish subjects, a gene frequency of .032 with a standard error of .004 was found. Among 2,305 normal subjects, 10 were found to be heterozygous for the 84GG allele, giving a gene frequency of .00217 with a standard error of .00096. No examples of the IVS2(+1) mutation were found among 1,256 samples screened, and no 1448C (L444P) mutations were found among 1,528 samples examined. Examination of the distribution of Gaucher disease gene frequencies in the general population shows that the ratio of 1226G mutations to 84GG mutations is higher than that in the patient population. This is presumed to be due to the fact that homozygotes for the 1226G mutation often have late-onset disease or no significant clinical manifestations at all. To bring the gene frequency in the patient population into conformity with the gene frequency in the general population, nearly two-thirds of persons with a Gaucher disease genotype would be missing from the patient population, presumably because their clinical manifestations were very mild.     

Gaucher disease: A G+1----A+1 IVS2 splice donor site mutation causing exon 2 skipping in the acid beta-glucosidase mRNA.

Gaucher disease is the most frequent lysosomal storage disease and the most prevalent Jewish genetic disease. About 30 identified missense mutations are causal to the defective activity of acid beta-glucosidase in this disease. cDNAs were characterized from a moderately affected 9-year-old Ashkenazi Jewish Gaucher disease type 1 patient whose 80-year-old, enzyme-deficient, 1226G (Asn370----Ser [N370S]) homozygous grandfather was nearly asymptomatic. Sequence analyses revealed four populations of cDNAs with either the 1226G mutation, an exact exon 2 (delta EX2) deletion, a deletion of exon 2 and the first 115 bp of exon 3 (delta EX2-3), or a completely normal sequence. About 50% of the cDNAs were the delta EX2, the delta EX2-3, and the normal cDNAs, in a ratio of 6:3:1. Specific amplification and characterization of exon 2 and 5' and 3' intronic flanking sequences from the structural gene demonstrated clones with either the normal sequence or with a G+1----A+1 transition at the exon 2/intron 2 boundary. This mutation destroyed the splice donor consensus site (U1 binding site) for mRNA processing. This transition also was present at the corresponding exon/intron boundary of the highly homologous pseudogene. This new mutation, termed "IVS2 G+1----A+1," is the first splicing mutation described in Gaucher disease and accounted for about 3.4% of the Gaucher disease alleles in the Ashkenazi Jewish population. The occurrence of this "pseudogene"-type mutation in the structural gene indicates the role of acid beta-glucosidase pseudogene and structural gene rearrangements in the pathogenesis of this disease.     

Linkage of the PvuII polymorphism with the common Jewish mutation for Gaucher disease.

We have localized the PvuII polymorphism of the glucocerebrosidase gene complex to intron 6 of the active gene. Using the polymerase chain reaction (PCR) to amplify intron 6 of DNA samples from Pv1.1-/Pv1.1+ individuals, we defined the mutation causing this polymorphism as a G----A single-base substitution at position 3931 of the active gene. By analyzing 54 unrelated Gaucher patients we show strong linkage disequilibrium between the Pv1.1- genotype and the common Jewish mutation 1226 causing the adult type of this disease. Gaucher disease patients heterozygous for the 1226 allele and one unidentified allele (1226/?), particularly those of Jewish ancestry, were predominantly of the Pv1.1-/PV1.1+ genotype. This suggests that one of the unknown alleles may be relatively common and linked to the Pv1.1+ genotype.     

Molecular analysis of Gaucher disease: distribution of eight mutations and the complete gene deletion in 27 patients from Germany

Gaucher disease is the most common lysosomal storage disease with a high prevalence in the Ashkenazi Jewish population but it is also present in other populations. The presence of eight mutations (1226G, 1448C, IVS2+1, 84GG, 1504T, 1604T, 1342C and 1297T) and the complete deletion of the β-glucocerebrosidase gene was investigated in 25 unrelated non-Jewish patients with Gaucher’s disease in Germany. In the Jewish population, three of these mutations account for more than 90% of all mutated alleles. In addition, relatives of two patients were included in our study. Restriction fragment length polymorphism analysis and sequencing of PCR products obtained from DNA of peripheral blood leukocytes was performed for mutation analysis. Gene deletion was detected by comparison of radioactively labelled PCR fragments of both the functional β-glucocerebrosidase gene and the pseudogene. Among the unrelated patients, 50 alleles were investigated and the mutations identified in 35 alleles (70%), whereas 15 alleles (30%) remained unidentified. The most prevalent mutation in our group of patients was the 1226G (370^Asn→Ser) mutation, accounting for 18 alleles (36%), followed by the 1448C (444^Leu→Pro) mutation, that was found in 12 alleles (24%). A complete gene deletion was present in two alleles (4%). The IVS1+2 (splicing mutation), the 1504T (463^Arg→Cys) as well as the 1342C (409^Asp→His) mutations were each present in one allele (2%). None of the alleles carried the 84GG (frameshift), 1604A (496^Arg→His) or the 1297T (394^Val→Leu) mutation. This distribution is different from the Ashkenazi Jewish population but is similar to other Caucasian groups like the Spanish and Portuguese populations. Our results confirm the variability of mutation patterns in Gaucher patients of different ethnic origin. All patients were divided into nine groups according to their genotype and their clinical status was related to the individual genotype. Genotype/phenotype characteristics of the 1226G, 1448C, and 1342C mutations of previous studies were confirmed by our results. Received: 19 November 1996 / Revised: 29 January 1997     

The major defect in Ashkenazi Jews with Tay-Sachs disease is an insertion in the gene for the alpha-chain of beta-hexosaminidase

The Ashkenazi Jewish population is enriched for carriers of a fatal form of Tay-Sachs disease, an inherited disorder caused by mutations in the alpha-chain of the lysosomal enzyme, beta-hexosaminidase A. Until recently it was presumed that Tay-Sachs patients from this ethnic isolate harbored the same alpha-chain mutation. This was disproved by identification of a splice junction defect in the alpha-chain of an Ashkenazi patient which could be found in only 20-30% of the Ashkenazi carriers tested. In this study we have isolated the alpha-chain gene from an Ashkenazi Jewish patient, GM515, with classic Tay-Sachs disease who was negative for the splice junction defect. Sequence analysis of the promoter region, exon and splice junctions regions, and polyadenylation signal area revealed a 4-base pair insertion in exon 11. This mutation introduces a premature termination signal in exon 11 which results in a deficiency of mRNA in Ashkenazi patients. A dot blot assay was developed to screen patients and heterozygote carriers for the insertion mutation. The lesion was found in approximately 70% of the carriers tested, thereby distinguishing it as the major defect underlying Tay-Sachs disease in the Ashkenazi Jewish population.     

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.     

Prevalence of nine mutations among Jewish and non-Jewish Gaucher disease patients.

The frequency of nine different mutated alleles known to occur in the glucocerebrosidase gene was determined in 247 Gaucher patients, of whom 176 were of Jewish extraction, 2 were Jewish with one converted parent, and 69 were of non-Jewish origin. DNA was prepared from peripheral blood, active glucocerebrosidase sequences were amplified by using the PCR technique, and the mutations were identified by using the allele-specific oligonucleotide hybridization method. The N37OS mutation appeared in 69.77% of the mutated alleles in Jewish patients and in 22.86% of the mutated alleles in non-Jews. The 84GG mutation, which has not been found so far among non-Jewish patients, existed in 10.17% of the disease alleles among Jewish patients. The IVS + 1 mutation constituted 2.26% of the disease alleles among Jewish patients and 1.43% among the non-Jewish patients. RecTL, a complex allele containing four single-base-pair changes, occurred in 2.26% of the alleles in Jewish patients and was found in two (1.43%) of the patients of non-Jewish extraction. Another complex allele, designated "RecNciI" and containing three single-point mutations, appeared in 7.8% of alleles of non-Jewish patients and in only two (0.56%) of the Jewish families. The prevalence of the L444P mutation among non-Jewish Gaucher patients was 31.43%, while its prevalence among Jewish patients was only 4.24%. The prevalence of two other point mutations--D409H and R463C--was 5.00% and 3.57%, respectively, among non-Jewish patients and was not found among the Jewish Gaucher patient population. The prevalence of the R496H mutation, found so far only among Jewish patients, was 1.13%. The results presented demonstrate that seven mutations identify 90.40% of the mutations among Jewish patients and that these seven mutations allow diagnosis of only 73.52% of the non-Jewish patients. Identification of additional mutant alleles will enhance the accuracy of carrier detection.     

Mutation and haplotype studies of familial Mediterranean fever reveal new ancestral relationships and evidence for a high carrier frequency with reduced penetrance in the Ashkenazi Jewish population

Familial Mediterranean fever (FMF) is a recessive disorder characterized by episodes of fever with serositis or synovitis. The FMF gene (MEFV) was cloned recently, and four missense mutations were identified. Here we present data from non-Ashkenazi Jewish and Arab patients in whom we had not originally found mutations and from a new, more ethnically diverse panel. Among 90 symptomatic mutation-positive individuals, 11 mutations accounted for 79% of carrier chromosomes. Of the two mutations that are novel, one alters the same residue (680) as a previously known mutation, and the other (P369S) is located in exon 3. Consistent with another recent report, the E148Q mutation was observed in patients of several ethnicities and on multiple microsatellite haplotypes, but haplotype data indicate an ancestral relationships between non-Jewish Italian and Ashkenazi Jewish patients with FMF and other affected populations. Among approximately 200 anonymous Ashkenazi Jewish DNA samples, the MEFV carrier frequency was 21%, with E148Q the most common mutation. Several lines of evidence indicate reduced penetrance among Ashkenazi Jews, especially for E148Q, P369S, and K695R. Nevertheless, E148Q helps account for recessive inheritance in an Ashkenazi family previously reported as an unusual case of dominantly inherited FMF. The presence of three frequent MEFV mutations in multiple Mediterranean populations strongly suggests a heterozygote advantage in this geographic region.     

Properties of beta-glucosidase in cultured skin fibroblasts from controls and patients with Gaucher disease.

Membrane-bound beta-glucosidase from cultured skin fibroblasts can be solubilized in an active form by treatment of membrane preparations with a mixture of Triton X-100 and sodium taurocholate. Several properties of the solubilized enzyme have been studied in fibroblasts from normal, healthy individuals and from 14 patients with different clinical forms of Gaucher disease. The patients studied were classified as follows: group 1 consisted of 10 chronic patients, all (with one exception) of Ashkenazi Jewish origin; group 2 consisted of three black American patients with severe visceral symptoms, manifest from early childhood, but with no apparent neurological involvement; and group 3 consisted of a single white patient with the classical infantile form of the disease. Specific beta-glucosidase activity ranged from 6.6% to 16.5% mean control value in group 1 patients and from 4.1% to 5.8% in groups 2 and 3. When compared with the enzyme from control fibroblasts, the enzyme from chronic Gaucher patients (group 1) was more rapidly inactivated at 50 degrees C, had an altered pH curve, was less effectively inhibited by deoxycorticosterone-beta-glucoside, and was more effectively inhibited by deoxycorticosterone. The enzyme from patients in groups 2 and 3 was qualitatively indistinguishable from the control enzyme in terms of these parameters. No differences in Km (4-methylumbelliferyl-beta-glucoside) or sedimentation coefficient were found between the beta-glucosidases from control and Gaucher cells. The results demonstrate that cells from Ashkenazi Jewish patients with the chronic form of Gaucher disease contain a structurally altered form of beta-glucosidase. This enzyme differs both from normal beta-glucosidase and from the residual enzyme in patients of different ethnic origin and with clinically more severe forms of the disease.     

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.     

Polymorphisms in the human glucocerebrosidase gene

The two glucocerebrosidase genes from a patient with Gaucher disease were cloned and 8850 bp of each sequenced. Each clone had a single nucleotide change accounting for the clinical glucocerebrosidase deficiency, an A to G transition at cDNA nucleotide 1226 in one clone, and an insertion of a G at cDNA nucleotide 84 in the other clone. Sequence analysis revealed that there were 11 additional differences between the two clones. The clone with the nt 1226 mutation was, as is always the case, Pv1.1- (polymorphic PvuII site present). The 84GG clone was Pv1.1+. Examination of 35 normal subjects and 51 Gaucher disease patients was consistent with the existence of only two major haplotypes. Two additional minor haplotypes were found, one in Africans and one in the white population. These represented additional mutations superimposed on the basic two haplotypes. Two unrelated patients with Gaucher disease seemed to be exceptions in the 5' end of the gene was heterozygous for the + and - haplotypes but the most 3' marker was homozygous. These patients are believed to have a gene deletion on one allele. In addition to these studies, we correct 28 minor errors in the originally published sequence.     

A population-genetic test of founder effects and implications for Ashkenazi Jewish diseases

A founder effect can account for the presence of an allele at an unusually high frequency in an isolated population if the allele is selectively neutral and if all copies are identical by descent with a copy that either was carried by a founder individual or arose by mutation later. Here, a statistical test of both aspects of the founder-effect hypothesis is developed. The test is performed by a modified version of a program that implements the Slatkin-Bertorelle test of neutrality. The test is applied to several disease-associated alleles found predominantly in Ashkenazi Jews. Despite considerable uncertainty about the demographic history of Ashkenazi Jews and their ancestors, available genetic data are consistent with a founder effect resulting from a severe bottleneck in population size between a.d. 1100 and a.d. 1400 and an earlier bottleneck in a.d. 75, at the beginning of the Jewish Diaspora. The relatively high frequency of alleles causing four different lysosomal storage disorders, including Tay-Sachs disease and Gaucher disease, can be accounted for if the disease-associated alleles are recessive in their effects on reproductive fitness.     

Two novel polymorphic sequences in the glucocerebrosidase gene region enhance mutational screening and founder effect studies of patients with Gaucher disease

Gaucher disease, an inherited glycolipid storage disorder, is caused by a deficiency of the catabolic enzyme glucocerebrosidase (EC 3.2.1.45). The gene for human glucocerebrosidase is located on chromosome 1q21 and has a highly homologous pseudogene situated 16 kb downstream. We report two novel polymorphic sequences in the glucocerebrosidase gene region: the first consists of a variable number of dinucleotide (CT) repeats located 3.2 kb upstream from the glucocerebrosidase gene, and the second is a tetranucleotide (AAAT) repeat found between the glucocerebrosidase gene and its pseudogene, 9.8 kb downstream from the functional gene. These polymorphic sequences, along with a previously reported PvuII polymorphism in intron 6 of the glucocerebrosidase gene, were analyzed in patients with Gaucher disease (n=106) and in two normal control populations, one of Ashkenazi Jewish ancestry (n=72) and the second comprising non-Jewish individuals (n=46). In these samples, strong linkage disequilibrium was found between mutations N370S, c.84–85insG, and R463C and specific haplotypes; no significant linkage disequilibrium was found when examining haplotypes of patients with the L444P mutation. Studies of these polymorphic sites in several instances also led to the recognition of genotyping errors and the identification of unusual recombinant alleles. These new polymorphic sites provide additional tools for mutational screening and founder effect studies of Gaucher disease. Received: 5 December 1998 / Accepted: 14 January 1999     

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.     

A gel electrophoretic assay for detecting the insertion defect in Ashkenazi Jewish carriers of Tay-Sachs disease

A simple, rapid, nonradioactive assay for detecting the 4-bp insertion defect found in the beta-hexosaminidase alpha-chain gene of 70% of the Ashkenazi Jewish carriers of Tay-Sachs disease is described. In this assay, DNA derived from such carriers serves as a template for the polymerase chain reaction. Following amplification of a 159-bp fragment of exon 11 inclusive of the insertion, a portion of the product is subjected to electrophoresis in a 4% NuSieve agarose minigel. Visualization of the DNA with ethidium bromide demonstrates that heterozygote carriers for the defect display two distinct bands. In contrast, DNA from carriers of the splice junction defect, a mutation found in 30% of the Ashkenazi Jewish carriers of Tay-Sachs disease, displays only one band.     

Rapid detection of the two common mutations in Ashkenazi Jewish patients with mucolipidosis type IV

Among Ashkenazi Jewish individuals with mucolipidosis IV (ML IV), two mutations in the ML IV gene, IVS3-1A --> G and delEX1-EX7, account for more than 95% of disease alleles. The reported method of genotyping for the delEX1-EX7 mutation involves a cumbersome multistep procedure. In the present study, a new simplified one-step procedure is described that detects this mutation in both patients and carriers. An improved procedure is also described for detection of the IVS3-1A --> G mutation. Using these improved procedures, we have characterized the ML IV mutant alleles in 27 patients and 95 of their relatives from 22 families, and in 123 unrelated and unaffected Ashkenazi Jewish controls. Of the 27 ML IV patients, 16 patients (59.3%) were found to be homozygous for the IVS3-1A --> G mutation and 1 patient (3.7%) homozygous for the delEX1-EX7 mutation. Additionally, 9 patients (33.3%) were compound heterozygotes for IVS3-1A --> G/delEX1-EX7. Among the 123 Ashkenazi Jewish controls, two individuals were identified as heteroallelic with one IVS3-1A --> G mutation (carrier frequency: approximately 1 in 61); none showed the delEX1-EX7 mutation. The modifications described here provide a more facile means of genotyping patients and carriers and expand the possibilities for screening at-risk populations.     

Age estimate of the N370S mutation causing Gaucher disease in Ashkenazi Jews and European populations: A reappraisal of haplotype data

The N370S mutation at the GBA locus on human chromosome 1q21, which causes Gaucher disease (GD), has a high frequency in the Ashkenazim and is the second-most-widespread GD mutation in the European non-Jewish population. A common ancient origin for the N370S mutation in the Ashkenazi Jewish and Spanish populations has been proposed on the basis of both a similar haplotype for associated markers and an age estimate that suggests that this mutation appeared several thousand years ago. However, a reappraisal of haplotype data, using the Risch formula properly along with a Luria-Delbrück setting of the genetic clock, allows identification of the likely origin of the N370S mutation in Ashkenazi Jews between the 11th and 13th centuries. This result is consistent with the estimated ages of other mutations that are frequent among Ashkenazim, with the exception of type II (Glu117Stop) factor XI deficiency, which is deemed to be >3000 years old, predating the separation of the Ashkenazi and Iraqi Jews. The present finding supports the hypothesis of a more recent origin for the N370S mutation and is consistent with both a founder chromosome transfer from Ashkenazim who assimilated in some European populations and a non-Jewish origin of the European N370S-bearing chromosomes.     

Asymptomatic Gaucher disease implications for large-scale screening

Gaucher disease, the most prevalent genetic disorder among Ashkenazi Jews, is characterized by significant phenotypic heterogeneity. Because seven mutations account for more than 96% of the disease alleles in this population, large-scale screening is feasible, and genotyping is commercially available. To date, only 400 Gaucher patients have been diagnosed in Israel, although 2,500 patients are predicted by gene frequency; hence, there is the probability that those uncovered by population screening will prove to be very mild or asymptomatic since these patients have generally escaped medical attention until now. We studied objective and subjective aspects in 68 asymptomatic/very mild patients, followed for a mean of 2.6 years, to assess the implications of identifying many more such patients if large-scale screening were to be implemented. We found there were no medically significant changes in disease severity during follow-up. The patients' subjective reports of their general health status were similar to those of normal subjects, and there were no significant changes in quality of life during follow-up. Our findings suggest that asymptomatic/mild Gaucher patients do not require frequent monitoring; there is no justification for "prophylactic" enzyme therapy in this group, and, hence, no rationale for large-scale screening in the Ashkenazi population. Furthermore, one needs to be concerned with the adverse effects of labeling large numbers of asymptomatic individuals as affected because of the potential for stigmatization and discrimination.     

Gaucher disease types 1, 2, and 3: differential mutations of the acid beta-glucosidase active site identified with conduritol B epoxide derivatives and sphingosine.

To elucidate the genetic heterogeneity in Gaucher disease, the residual beta-glucosidase in cultured fibroblasts from affected patients with each of the major phenotypes was investigated in vitro and/or in viable cells by inhibitor studies using the covalent catalytic site inhibitors, conduritol B epoxide or its bromo derivative, and the reversible cationic inhibitor, sphingosine. These studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to these inhibitors. Group A residual enzymes had normal I50 values (i.e., the concentration of inhibitor that results in 50% inhibition) for the inhibitors and normal or nearly normal t1/2 values for conduritol B epoxide. All neuronopathic (types 2 and 3) and most non-Jewish nonneuronopathic (type 1) patients had group A residual activities and, thus, could not be distinguished by these inhibitor studies. Group B residual enzymes had about four- to fivefold increased I50 values for the inhibitors and similarly increased t1/2 values for conduritol B epoxide. All Ashkenazi Jewish type 1 and only two non-Jewish type 1 patients had group B residual activities. The differences in I50 values between groups A and B also were confirmed by determining the uninhibited enzyme activity after culturing the cells in the presence of bromo-conduritol B epoxide. Group C residual activity had intermediate I50 values for the inhibitors and represented a single Afrikaner type 1 patient: this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. These inhibition studies indicated that: Gaucher disease type 1 is biochemically heterogeneous, neuronopathic and non-Jewish nonneuronopathic phenotypes cannot be reliably distinguished by these inhibitor studies, and the Ashkenazi Jewish form of Gaucher disease type 1 results from a unique mutation in a specific active site domain of acid beta-glucosidase that leads to a defective enzyme with a decreased Vmax.