Polymerase chain reaction detection of two novel human N-acetylgalactosamine-6-sulfate sulfatase gene polymorphisms by single-strand conformation polymorphism analysis or by StyI and StuI cleavages

Molecular analysis in a GALNS study cohort of 15 Tunisian patients: description of a novel mutation

Background

Mucopolysaccharidosis type IVA (MPS IVA) is an autosomal recessive disease caused by the deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The purpose of this study was to analyze the GALNS mutations and the haplotypes associated.

Methods

Mutation screening of the GALNS gene was performed by direct sequence analysis using DNA samples from 15 unrelated Tunisian MPS IVA patients. We also analyzed the haplotypes associated with the novel mutation and with the other reported GALNS mutations.

Results

We have identified an unreported missense mutation p.D288G (c.863A > G) in one patient, the most frequently c.120 + 1G > A (IVS1 + 1G > A) mutation in eleven MPS IVA patients and three previously reported mutations p.G66R, p.A85T and p.R386C on the other MPS IVA patients. All the studied patients were homozygous for these identified mutations. Bioinformatics analysis predicted the novel mutation as being probably pathogenic. These findings with the unobserved p.D288G mutation in controls subjects, suggested that it is a disease-causing mutation, which was correlated with the severe phenotype observed in the patients. We have found that the two GALNS unreported and reported mutations, respectively p.D288G and p.R386C, were associated with a common and specific haplotype.

Conclusion

Our results were in agreement with previous reports from Tunisia, suggesting, on one hand the genotype/phenotype correlations in MPS IVA patients and the other hand the haplotype analyses were useful for determination of mutation origin in Tunisian population.

Polymorphisms in Tunisian patients with N-acetylgalactosamine-6-sulfate sulfatase gene deficiency: implication in Morquio A disease

Mucopolysaccharidosis type IVA or Morquio A syndrome is characterized by the lack of N-acetylgalactosamine-6-sulfate-sulfatase and the accumulation of keratan sulfate and chondroitin-6-sulfate in the lysosomes. At least, 148 mutations and 16 polymorphisms were identified in the GALNS gene.

The aim of this study was the screening of polymorphisms within 7 patients recruited from many regions of Tunisia in order to determine the haplotypes and their association with the mutations previously reported.

Patients and methods

We have used the PCR sequencing to analyse the different haplotypes and to identify the polymorphisms within 7 affected MPS IVA patients.

Results

Nine GALNS polymorphisms were detected in the 7 studied patients. Five of these polymorphisms are within the GALNS gene exons. Six polymorphisms have been previously described and used for linkage analysis in MPS IVA patients and determination of haplotypes. We have identified two novel heterozygous polymorphisms in intron 13 and intron 3

Conclusion

Polymorphisms may be useful for carrier detection and prenatal diagnosis in informative families whose specific mutations have not been identified. The determination of haplotypes can also determine the origin of some mutations in a population.

Mucopolysaccharidosis type IV: N-acetylgalactosamine-6-sulfatase mutations in Tunisian patients

Mucopolysaccharidosis type IVA (MPS IVA; OMIM #253000) or Morquio A syndrome is an autosomal recessive inborn error resulting from the deficient activity of the lysosomal enzyme, N-acetylgalactosamine-6-sulfatase (GALNS), and the progressive lysosomal accumulation of sulfated glycosaminoglycans. Clinically, the severe form of this lysosomal storage disease is characterized by a characteristic severe bone dysplasia and normal intelligence. To date, a variety of mutations have been associated with the severe MPS IVA phenotype. Here, we report the GALNS mutations in six severe MPS IVA patients from four unrelated Tunisian families. For mutation detection, each of the 14 exons and adjacent intron-exon junctions of the GALNS gene were sequenced after PCR-amplification from genomic DNA. Two novel mutations were identified: a G to A transition in the conserved 5' donor splice site of intron 1 (GACgt-->GACat: designated IVS1(+1g-->a)) and a G to C transversion in codon 66 of exon 2 predicting a glycine to arginine substitution (G66R). The IVS1(+1g-->a) mutation was homozygous in five similarly affected patients from three presumably unrelated families, but haplotype analysis suggested a common ancestor. The affected patient in the fourth family was homozygous for the G66R mutation. These are the first GALNS mutations causing severe MPS IVA disease identified in Tunisia. These molecular findings provide genotype/phenotype correlations, and permit accurate carrier detection, prenatal diagnosis, and counseling for MPS IVA disease in Tunisia where first cousin consanguineous mating remains frequent.

Mucopolysaccharidosis IVA: a comparative study of polymorphic DNA haplotypes in the Caucasian and Japanese populations

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulphate sulphatase (GALNS). The genetic heterogeneity at the GALNS locus was studied in 62 mutant alleles and 376 normal alleles in the Caucasian population and also in 40 mutant and 100 normal alleles in the Japanese population. For this study, six different restriction fragment length polymorphisms (RFLPs) at the GALNS locus were analysed to search for the frequency of each RFLP produced by StyI, SphI, RsaI, HaeIII, StuI and HapII restriction endonucleases. We detected a total of 27 haplotypes in the Caucasian and Japanese population. Of these 27 haplotypes, 18 haplotypes were present in the Caucasian population and the most common of these was haplotype 1 (ABHcde) in both mutant and normal alleles. In contrast, in the Japanese population we found 20 of the 27 haplotypes and the most common in mutant and normal alleles was haplotype 2 (abhcDE). Within these two populations a parent in the MPS IVA family has an average probability of greater than 77% (in the Caucasian population 77.27% and in the Japanese population 78.26%) of being heterozygous, and hence informative for linkage, at one or more GALNS RFLP sites. Our results delineate the molecular heterogeneity of MPS IVA haplotypes, as well as their significant interpopulation variation, and make prenatal diagnosis and carrier detection possible in the majority of families with one affected child.

Mucopolysaccharidosis type IVA: common double deletion in the N-acetylgalactosamine-6-sulfatase gene (GALNS)

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive disorder caused by a deficiency in N-acetylgalactosamine-6-sulfatase (GALNS). We found two separate deletions of nearly 8.0 and 6.0 kb in the GALNS gene, including some exons. There are Alu repetitive elements near the breakpoints of the 8.0-kb deletion, and this deletion resulted from an Alu-Alu recombination. The other 6.0-kb deletion involved illegitimate recombinational events between incomplete short direct repeats of 8 bp at deletion breakpoints. The same rearrangement has been observed in a heteroallelic state in four unrelated patients. This is the first documentation of a common double deletion a gene that is not a member of a gene cluster.

Mucopolysaccharidosis IVA: polymorphic haplotypes and informative RFLPs in the Japanese population

Seven different restriction fragment length polymorphisms (RFLPs) at the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) locus were analyzed using Southern blotting and polymerase chain reaction based techniques to search for the frequency of each RFLP produced by StyI, SphI, HaeIII, StuI, HapII, XhoI, and BamHI restriction endonucleases, respectively, in 36 mutant alleles, including two sibling cases and 100 normal alleles. Calculation of heterozygosity indexes showed that these RFLPs were polymorphic, ranging from 0.31 to 0.69 in mucopolysaccharidosis IVA (MPS IVA) patients compared with 0.21 to 0.65 in normal individuals. There was some significant difference in several RFLPs and in the combination with four kinds of RFLPs (SphI, StuI, HapII, XhoI polymorphisms). The normal alleles were composed of 13 different RFLPs haplotypes; the most common among the Japanese population carrying normal alleles was haplotype 8 (bDEF1) (31.3%), the others being dispersed. The same haplotype 8 was the most frequent in the mutant alleles (44.4%), with seven further haplotypes. These findings revealed the striking variety of polymorphic haplotypes in the MPS IVA gene. By using these five kinds of RFLPs, we examined the theoretical informativity of haplotype analysis in heterozygote detection in nine unrelated MPS IVA families and ten unrelated normal families. All the members of the MPS IVA families studied were diagnosed as a patient, carrier, or non-carrier. We propose that prenatal diagnosis or family analysis in cases in which mutations have not been characterized is now feasible.