[Molecular diagnosis of Gaucher disease in Tunisia]

Gaucher disease is a lysosomal storage disorder caused by a deficiency of the enzyme acid β-glucosidase. In order to determine the mutation spectrum in Tunisia, we performed recurrent mutation screening in 30 Tunisian patients with Gaucher disease. Screening of recurrent mutation by PCR/RFLP and direct sequencing had shown that N370S was the most frequent mutation (22/50 mutant alleles, 44%), followed by L444P mutation, which is found in 16% (8/50 mutant alleles). The recombinant allele (RecNciI) represented 14%. Our findings revealed that the genotype N370S/RecNciI was mosst frequent in patients with childhood onset and it was associated with severe visceral involvement. The screening of these three mutations provided a simple tool for molecular diagnosis of Gaucher disease in Tunisian patients and allowed also genetic counselling for their family members.

[Mutation spectrum of Gaucher disease in Tunisia: high frequency of N370S/Rec NciI compound heterozygous]

Gaucher disease is the most common lysosomal storage disorder, it results from the inherited deficiency of the enzyme glucocerebrosidase, the accumulation of its substrate causes many clinical manifestations. Since the discovery of GBA gene, more than 200 different mutations have been identified, but only handful mutations are recurrent (N370S, L444P and c.84insG). In order to determine the mutation spectrum in Tunisia, we performed recurrent mutation screening in ten unrelated Tunisian children with Gaucher disease. Screening of recurrent mutation by PCR/RFLP and direct sequencing, has shown that N370S is the most frequent mutation (6/20 mutant alleles, 30%), followed by recombinant allele (RecNciI) which is found in five patients (5/20 mutant alleles, 25%), the L444P mutation represent 20% (4/20 mutant alleles). Our findings revealed that five among ten studied patients, were compound heterozygous N370S/RecNciI (50%). The screening of these mutations provides a simple tool for molecular diagnosis of Gaucher disease in Tunisian patients and allows also genetic counselling for their family members.

Allelic frequency determination of the 24-bp chitotriosidase duplication in the Portuguese population by real-time PCR

Chitotriosidase is a human chitinase produced by macrophages. Its enzymatic activity is markedly elevated in serum of patients suffering from lysosomal storage disorders, as well as other diseases in which macrophages are activated. Therefore, it is a useful tool as a secondary marker in the diagnosis of several disorders including Gaucher disease type 1 and Niemann-Pick disease. The determination of chitotriosidase levels as a diagnosis complement in some lysosomal storage disorders and in enzyme replacement therapy follow-up of Gaucher disease patients is of great importance. However, the fact that a mutation caused by a 24-bp duplication in the CHIT1 gene resulting in deficiency of plasma chitotriosidase activity is very frequent makes the establishment of the frequency of this mutation in different population groups necessary. Furthermore, in order to validate the use of chitotriosidase activity as a marker, it is indispensable to screen individuals for this particular mutation. In this work, we present the results of a study where the allelic frequency of the above mentioned CHIT1 gene mutation was determined in the Portuguese population by real-time PCR. The frequency of carriers encountered in this sample of Portuguese individuals was of 37%.

Adult-onset neuronopathic form of Gaucher's disease: a case report

We report a patient with Gaucher's disease (GD) developing prominent neurological abnormalities in adult life confirming the existence of an adult neuronopathic form of GD. In this adult-onset form, an akinetic-rigid syndrome poorly responsive to dopatherapy, supranuclear gaze palsy, myoclonic jerks, seizures, cerebellar ataxia, cognitive and psychotic disturbances are frequent manifestations. The widely used clinical classification seems inadequate since it does not consider this rare form of GD. Until further understanding of the pathogenesis of the disease is achieved it is not possible to predict accurately which patients will or will not have late-onset nervous system involvement.

Niemann-Pick type C disease: NPC1 mutations associated with severe and mild cellular cholesterol trafficking alterations

Niemann-Pick type C disease (NPC) is a rare neurodegenerative disorder characterised by lysosomal/late endosomal accumulation of endocytosed unesterified cholesterol and delayed induction of cholesterol homeostatic reactions. The large majority of mutations in the NPC1 gene described thus far have been associated with severe cellular cholesterol trafficking impairment (classic biochemical phenotype, present in about 85% of NPC patients). In our population of 13 unrelated NP-C1 patients, among which 12 were of Portuguese extraction, we observed an unusually large proportion of families presenting mild alterations of intracellular cholesterol transport (variant biochemical phenotype), without strict correlation between the biochemical phenotype and the clinical expression of the disease. Mutational studies were carried out to compare molecular lesions associated with severe and mild cholesterol traffic impairment. Levels of NPC1 protein were studied by Western blot in cultured fibroblasts of four patients with homozygous mutant alleles. Ten novel mutations were identified (Q92R, C177Y, R518W, W942C, R978C, A1035V, 2129delA, 3662delT, IVS23+1 G>A and IVS16-82 G>A). The mutational profile appeared to be correlated with the biochemical phenotype. Splicing mutations, I1061T and A1035V, corresponded to "classic" alleles, while three missense mutations, C177Y, R978C and P1007A, could be defined as "variant" alleles. All "variant" mutations described so far appear to be clustered within the cysteine-rich luminal loop between TM 8 and 9, with the remarkable exception of C177Y. The latter mutant allele, at variance with P1007A, was correlated to a decreased level of NPC1 protein and a severe course of the disease, and disclosed a new location for "variant" mutations, the luminal loop located at the N-terminal end of the protein.

Metachromatic leucodystrophy in Portugal-finding of four new molecular lesions: C300F, P425T, g.1190-1191insC, and g.2408delC. Mutations in brief no. 232. Online

The mutation identification rate achieved in the study of Portuguese MLD patients was found to be extremely high (100%), thus revealing the power of the association of vertical and horizontal PCR-SSCA. The identification of new mutations adds to the large number of mutations already described to be associated to MLD. Nevertheless, mutation g.1238G>A has been found in most of the Portuguese patients, either in homozygosity or heterozygosity, suggesting this mutation to be more common in Portuguese patients than in patients with other ethnic backgrounds. Two new missense mutations (C300F and P425T) were found to be associated to late infantile and juvenile forms, respectively. Two novel microlesions (g.1190-1191insC, g.2408delC) were identified in two late infantile patients. It should be noted that both C300F and g.2408delC were detected in homozygosity. The approach used and the results here presented may provide useful information for the study of other MLD patients, as well as new insights about the effect of mutations, such as C300F, in the structure/function of ARSA.

Gaucher disease: the origins of the Ashkenazi Jewish N370S and 84GG acid beta-glucosidase mutations

Type 1 Gaucher disease (GD), a non-neuronopathic lysosomal storage disorder, results from the deficient activity of acid beta-glucosidase (GBA). Type 1 disease is panethnic but is more prevalent in individuals of Ashkenazi Jewish (AJ) descent. Of the causative GBA mutations, N370S is particularly frequent in the AJ population, (q approximately .03), whereas the 84GG insertion (q approximately .003) occurs exclusively in the Ashkenazim. To investigate the genetic history of these mutations in the AJ population, short tandem repeat (STR) markers were used to map a 9.3-cM region containing the GBA locus and to genotype 261 AJ N370S chromosomes, 60 European non-Jewish N370S chromosomes, and 62 AJ 84GG chromosomes. A highly conserved haplotype at four markers flanking GBA (PKLR, D1S1595, D1S2721, and D1S2777) was observed on both the AJ chromosomes and the non-Jewish N370S chromosomes, suggesting the occurrence of a founder common to both populations. Of note, the presence of different divergent haplotypes suggested the occurrence of de novo, recurrent N370S mutations. In contrast, a different conserved haplotype at these markers was identified on the 84GG chromosomes, which was unique to the AJ population. On the basis of the linkage disequilibrium (LD) delta values, the non-Jewish European N370S chromosomes had greater haplotype diversity and less LD at the markers flanking the conserved haplotype than did the AJ N370S chromosomes. This finding is consistent with the presence of the N370S mutation in the non-Jewish European population prior to the founding of the AJ population. Coalescence analyses for the N370S and 84GG mutations estimated similar coalescence times, of 48 and 55.5 generations ago, respectively. The results of these studies are consistent with a significant bottleneck occurring in the AJ population during the first millennium, when the population became established in Europe.

Gaucher disease: expression and characterization of mild and severe acid beta-glucosidase mutations in Portuguese type 1 patients

Type 1 Gaucher disease (GD), the most prevalent lysosomal storage disease, results from the deficient activity of acid beta-glucosidase. Molecular analysis of 12 unrelated Portuguese patients with type 1 GD identified three novel acid beta-glucosidase mutations (F109V, W184R and R395P), as well as three previously reported, but uncharacterized, lesions (R359Q, G377S and N396T). The type 1 probands were either heteroallelic for the well-characterized common lesion, N370S, and the F109V, W184R, R359Q or N396T lesions or homoallelic for the G377S or N396T mutations. Expression of the W184R, R359Q and R395P mutations revealed very low specific activities based on cross-reacting immunologic material (CRIM SAs of 0.0004, 0.016 and 0.045, respectively), consistent with their being found only in type 1 patients who had a neuroprotective N370S allele. In contrast, the F109V, G377S and N396T alleles had significant acid beta-glucosidase activity (CRIM specific activities of 0.15, 0.17, 0.14, respectively), in agreement with their being mild type 1 alleles. Thus, these studies identified additional acid beta-glucosidase mutations in the Portuguese population and demonstrated that the G377S and N396T mutations were neuroprotective, consistent with the mild clinical phenotypes of the type 1 patients who were homoallelic for the G377S and N396T lesions.

T cell numbers relate to bone involvement in Gaucher disease

The major elements of bone pathology in Gaucher disease are a failure of osteoclast and osteoblast function, resulting in osteopenia and also osteonecrosis. T lymphocytes have recently been found to be involved in the regulation of osteoblast/osteoclast activity in vitro. In the present report the peripheral blood T major lymphocyte subsets were investigated in a group of genotyped type 1 Gaucher disease patients. A total of 31 patients were studied: 21 non-splenectomized (5 N370S homozygotes) and 10 splenectomized (of whom 1 was a N370S homozygote). The results show that non-splenectomized patients present a decrease in absolute numbers of peripheral blood T lymphocytes, specially the CD4+ T subset. However, when patients were analyzed with respect to the presence of bone disease, the number of CD8+ T lymphocytes was found to be statistically significantly lower in patients presenting bone involvement. Furthermore, lower numbers of CD8+ T lymphocytes were significantly correlated with higher levels of plasma tartrate resistant acid phosphatase (TRAP) activity, a putative marker of osteoclast cell activity. These in vivo findings are in agreement with the results reached in vitro by others. They provide an additional marker of disease severity in Gaucher disease. In the group of genotyped Gaucher disease patients, the majority of the N370S homozygous patients presented a clinically milder phenotype, including the absence of bone involvement, confirming earlier reports predicting that a number of these patients may remain undiagnosed. Collectively the homozygosity for the N370S mutation and normal T cell numbers may provide additional markers for the clinical heterogeneity of Gaucher disease.

Distinct haplotype in non-Ashkenazi Gaucher patients with N370S mutation

A new polymorphism, in intron 7 of glucocerebrosidase gene, has been identified in Gaucher Disease patients. It seems to appear only in Pv1.1- alleles bearing the N370S mutation. This new sub-haplotype was only identified in Portuguese patients, of origins spanning all of the Portuguese continental territory. This finding indicates that, in the Portuguese, mutation N370S has existed in the context of two slightly different haplotypes and thus must be relatively ancient.

Gaucher disease: N370S glucocerebrosidase gene frequency in the Portuguese population

In the Portuguese population the most frequent form of Gaucher disease is type 1. The N370S glucocerebrosidase gene mutation accounts for 63% of mutated alleles. The frequency of this mutation was accurately determined in the Portuguese population, which does not present an Ashkenazi Jewish genetic background. A gene frequency of 0.0043, with 95% confidence limits between 0.0023 and 0.0063, was obtained studying the genomic DNA of 2000 blood cards randomly sampled from the national neonatal screening program. On the basis of this frequency a significantly high number of homozygotes for the N370S mutation should be expected in the Portuguese population. This finding supports the idea that the majority of homozygotes for this mutation present a very mild clinical phenotype and remain undiagnosed.

Molecular characterisation of type 1 Gaucher disease families and patients: intrafamilial heterogeneity at the clinical level

Type 1 Gaucher disease families were studied in an attempt to establish a phenotype/genotype correlation in affected persons and also to identify carriers accurately. In the Portuguese type 1 Gaucher patients, screening for mutations N370S, L444P, R463C, and 1066 + 1 G-->A allowed the identification of 85% of the alleles among unrelated patients. A subclinical case with genotype N370S/1066 + 1 G-->A was identified in one family in which there were three other symptomatic sibs. To our knowledge this is the first subclinical case with a genotype other than N370S/N370S. No genotype-phenotype correlation could be established and considerable clinical heterogeneity was found even among sibs with the same genotype. The data collected on the origins of the Gaucher families indicated two areas in northern Portugal where a higher frequency of the disease may be expected to exist.

The N370S mutation in the glucocerebrosidase gene of Portuguese type 1 Gaucher patients: linkage to the PvuII polymorphism

The mutation N370S accounts for 63% of the mutated glucocerebrosidase alleles of Portuguese type 1 Gaucher patients. It has been shown previously that this mutation is linked to the Pv1.1- form of the PvuII polymorphism and suggested that the N370S mutation in glucocerebrosidase alleles has an Ashkenazi Jewish origin. We have found that in Portuguese type 1 Gaucher patients this mutation is also invariably associated with the Pv1.1- haplotype, despite the fact that there is no evidence of Ashkenazi Jewish background in this population.

Identification of Gaucher disease carriers: glucocerebrosidase antigen and DNA analysis

Detection of Portuguese carriers for Gaucher disease with urine samples as a source of enzyme was carried out using an immunological procedure employing an anti-glucocerebrosidase monoclonal antibody and by DNA analysis for the presence of the two glucocerebrosidase mutations most frequently found in Portuguese Gaucher patients. Patients, obligate and putative carriers, and individuals unrelated to patients were analyzed. It was found that the vast majority of carriers for the two tested mutations (N370S and L444P), as well as obligate carriers for as yet unidentified mutations, could be distinguished from control subjects with this relatively easy and economic immunological procedure. Furthermore, results obtained for control subjects suggested a high frequency of carriers for the N370S mutation in the Portuguese population. It is concluded that this procedure may be useful in mass screening for carrier detection prior to DNA analysis, particularly in the study of non-Ashkenazi populations in which a significant number of mutations associated with Gaucher disease remain unidentified.

Type 1 Gaucher disease: molecular, biochemical, and clinical characterization of patients from northern Portugal

We report the study of 16 catholic type 1 Gaucher disease patients originating from a well-defined region in the north of Portugal where a relatively high incidence is observed. The patients were screened for mutations: 3060G-->A, 5841A-->G, 5976C-->G, and 6433T-->C, which enabled the identification of 27 of the 32 mutated alleles. Four different genotypes were identified, namely 5841G/6433C (n = 6), 5841G/5841G (n = 5), 5841G/? (n = 4), and 6433C/? (n = 1). All but one of the patients carried at least one 5841G mutated allele, making its frequency 62.5%, which is similar to that described for Ashkenazi Jewish patients. The 5841G homozygotes presented an overall milder clinical profile, whereas no clear genotype/phenotype correlation could be established for heterozygous patients. On the basis of residual glucocerebrosidase activity, no distinction could be made between 5841G homozygotes and 5841G/6433C compound heterozygotes. Patients that had at least one 5841G allele (encoding the Ser 370 mutated enzyme) all presented a cell-type-specific residual glucocerebrosidase activity as well as an increased molecular activity when measured in the presence of the physiological activators.