The effect of four mutations on the expression of iduronate-2-sulfatase in mucopolysaccharidosis type II.

Mucopolysaccharidosis type II (Hunter syndrome; OMIM 309900) is a rare X-linked recessive lysosomal storage disorder caused by the deficiency of the enzyme iduronate-2-sulfatase (IDS; EC 3.1.6.13). Different alterations at the IDS locus, mostly missense mutations, have been demonstrated, by expression study, as deleterious, causing significant consequences on the enzyme function or stability. In the present study we report on the results of the transient expression of the novel K347T, 533delTT, N265I and the already described 473delTCC (previously named DeltaS117) mutations in the COS 7 cells proving their functional consequence on IDS activity. This type of information is potentially useful for genotype-phenotype correlation, prognosis and possible therapeutic intervention.

Prenatal diagnosis of Pelizaeus-Merzbacher disease: detection of proteolipid protein gene duplication by quantitative fluorescent multiplex PCR.

A prenatal diagnosis of Pelizaeus-Merzbacher disease (PMD) resulting from proteolipid protein gene (PLP) duplication was performed by a quantitative fluorescent multiplex PCR method. PLP gene copy number was determined in the proband, the pregnant mother, the male fetus and two aunts. Small amounts of genomic DNA extracted from peripheral blood and from chorionic villi were used. The fetus, in common with the proband, was identified as PMD-affected being a carrier of the PLP gene duplication, inherited from the mother, while the two aunts were non-carriers. The data obtained were confirmed by segregation analysis of a PLP-associated dinucleotide-repeat polymorphism amplified by the same multiplex PCR.

Molecular analysis of 40 Italian patients with mucopolysaccharidosis type II: New mutations in the iduronate-2-sulfatase (IDS) gene.

Mucopolysaccharidosis type II (MPS2, or Hunter syndrome), rare X-linked lysosomal storage disorder, results from deleterious mutations in the iduronate-2-sulfatase (IDS) gene. We report here the mutational analysis of a total of 40 unrelated Italian MPS II patients ranging from mild to severe phenotype. We are able to assign the genotype to 29 of them (72.5%), identifying 22 different mutations, five of which are unpublished (c.533delTT, W12X, N265I, c.1131-1142del, c.1131-1305del). A total of 55.2% of the molecularly characterised patients resulted from missense mutations, 20.7% from nonsense mutations, and another 13.8% of patients from small deletions (<20pb) or splice mutations, whereas 10.3% of the cases carried major structural alterations such as large deletion and rearrangements. The results reported here support the evidence of the mutational heterogeneity of the IDS gene as well as the difficulty to correlate genotype and phenotype in the patients with MPSII. However, the molecular characterisation of the patients is advantageous, making the carrier detection feasible for the females in the family at risk and improving the reliability of prenatal diagnosis techniques. Moreover, it provides a good foundation for therapeutic strategies.

Aberrant splicing at catalytic site as cause of infantile onset glycogen storage disease type II (GSDII): molecular identification of a novel IVS9 (+2GT-->GC) in combination with rare IVS10 (+1GT-->CT).

Glycogen storage disease type II (GSDII) results from deleterious mutations in acid alpha-glucosidase gene. To date several mutant alleles have been studied including missense and nonsense mutations, insertions, small and large deletions as well as splice site mutations. Apart from IVS1 (- 13-->G), 525delT, and Delta18, the other mutations are rare and often unique to single patients. Moreover, the molecular findings also observed in the different ethnic groups makes it difficult to attempt to correlate genotype and phenotype to explain the origin of clinical variability. Even though there are no conclusive genotype phenotype correlations, the in frame splice site mutations identified up until now have been found associated with the juvenile/adult onset of GSDII. In this study we describe a novel in frame splicing defect, IVS9 (+2GT-->GC), identified in combination with the rare IVS10 (+1GT-->CT) mutation in a patient with classic infantile GSDII disease. Because both mutations occur at the catalytic site region, it is likely that the alteration of both catalytic function and steric conformation of the enzyme may be responsible for the most severe form of the disease.

Identification of a novel recombinant allele in three unrelated Italian Gaucher patients: implications for prognosis and genetic counseling.

Gaucher disease (GD) results from deleterious mutations in the glucocerebrosidase gene. The relatively high frequency of some of these, especially at cDNA nucleotide 1226G (N370S) and at cDNA nucleotide 1448C (L444P), has led to the development of rapid screening techniques that can sometimes be misleading. In this report, we describe a novel rearrangement between the glucocerebrosidase gene and its pseudogene, identified as a consequence of a discrepancy between the genotype, homozygous for the common 1226G mutation, of an Italian patient with type 1 Gaucher disease, and the absence of the 1226G allele in her daughter. Additional investigations went on to reveal a novel recombinant allele beginning in intron 6 and extending through the rest of the coding sequence. Italian GD patients found homozygous for a specific mutation or with one or both alleles still unknown were further investigated and the novel recombinant allele was identified in an adult type 1 patient previously genotyped 1226G/1226G and in a young patient with an unknown genotype. The detection of this allele in three unrelated GD patients originating from the same geographic area in central Italy suggested a founder effect. This study emphasizes the implications of an accurate genotyping for the prognostic value of glucocerebrosidase genotype and reliable genetic counseling.

Evidence for a founder effect in Sicilian patients with glycogen storage disease type II.

Glycogen storage disease type II (GSD II) is an autosomal recessive inherited disorder due to the deficiency of the enzyme acid alpha-glucosidase, which causes an accumulation of glycogen in lysosomes. The deletion of exon 18 (delta 18) is a frequent mutation associated with a severe phenotype. We analyzed 25 Italian patients, 5 of whom were found to be delta 18 carriers. All these 5 patients came from Catania, a town in Sicily. We report on the analysis of 5 intragenic single-point polymorphic markers in the delta 18 patients and on the subsequent characterization of a delta 18-associated haplotype. The frequency of this haplotype in GSD II patients and normal individuals was 1 and 0.196, respectively (chi(2) = 20.9; p < 0.001). The high frequency of the delta 18 allele in this Italian subpopulation is likely to be due to a founder effect.

A deletion involving exons 2-4 in the iduronate-2-sulfatase gene of a patient with intermediate Hunter syndrome.

A large deletion in the iduronate-2-sulfatase (IDS) gene has been found in a patient affected by an intermediate form of Hunter syndrome (mucopolysaccharidosis II). The deletion involves exons 2-4, the breakpoints lying respectively in intron 1, at position 376, and in intron 4, at position 5725. cDNA analysis revealed a direct exon 1-exon 5 junction due to the deletion resulting in a frameshift mutation.