Molecular investigation of mucopolysaccharidosis type II (Hunter syndrome) in man

Abstract: Mucopolysaccharidosis type II or Hunter syndrome is a rare lysosomal storage disorder caused by a deficiency in the enzyme iduronate-2-sulfatase (IDS). The disorder is inherited in an X-linked recessive fashion and has a broad spectrum of clinical phenotypes ranging from severe to mild. Different mutations in the IDS locus affecting enzyme function or stability explain a wide spectrum of clinical phenotypes.The aim of the work described in this thesis is to identify and analyse the mutations in the human iduronate-2-sulfatase (IDS) gene resulting in the development of Hunter syndrome. The DNA samples from 63 unrelated patients were analysed by Southern blot analysis, PCR, RT-PCR, SSCP and DNA sequencing. Among 55 mutant alleles, there were 33 missense/nonsense mutations, 6 mutations affecting splicing, and 12 major structural alterations resulting in various rearrangements. Of the 45 different mutations 26 were novel and unique. The study of large group of patients originated from Russia anddiagnosed by the same clinician allowed us to investigate the correlation between genotype and phenotype in the Hunter syndrome.The structural rearrangements and deletions of the entire IDS gene are observed in about 20% of the patients, suggesting the presence of recombinational "hotspots" in the locus. We have isolated and characterised the recombinational junctions from 9 unrelated MPSII patients with structural rearrangements in the IDS gene. It was shown that the IDS gene is frequently involved in the homologous recombination with the IDS-2 pseudogene resulting in inversions. Moreover, the presence of homologous regions in the IDS locuspossibly promotes nonhomologous recombination resulting in various intragenic deletions and complex rearrangements of the IDS gene. The models explaining recombinational events are proposed.The data reported in this thesis contributes to our understanding of the nature of mutation events and provides valuable insights into the mechanisms of DNA recombination. The knowledge of the IDS gene defects permits direct detection of carriers of that mutation, allows to make the prognostic predictions about clinical severity and gives us information about the functionally important parts of the iduronate-2-sulfatase.