MOLECULAR GENETICS OF IDURONATE SULFATASE DEFICIENCIES

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A deficiency of the lysosomal enzyme iduronate sulfatase is found in two genetic diseases, Hunter syndrome and multiple sulfatase deficiency. Hunter syndrome, which is inherited as an X-linked recessive disorder, is due to the deficiency of iduronate sulfatase. The two forms of Hunter syndrome, mild and severe, have nearly total deficiency of iduronate sulfatase activity and cannot be distinguished biochemically. No definitive treatment is available for most patients with mucopolysaccharidoses (MPS), although these disorders are potential candidates for gene therapy. Iduronate sulfatase is also known to be decreased in multiple sulfatase deficiency along with at least six other sulfatases. This disorder combines features of MPS and metachromatic leukodystrophy. The major goals of this proposal are to determine the nature of the genetic defects in patients with mild and severe Hunter syndrome and multiple sulfatase deficiency at the protein and molecular levels. The biosynthesis of the radiolabeled mutant iduronate sulfatase proteins will be studied in fibroblasts using immunoprecipitation and polyacrylamide gel electrophoresis. The molecular cloning of a cDNA for human iduronate sulfatase will utilize one of two possible approaches. A gt11 human placenta cDNA expression library will be screened with antibody or an oligonucleotide probe will be constructed from amino acid sequence data. The isolated cDNA clone will be used to characterize the defects in Hunter syndrome and multiple sulfatase deficiency at the genomic and mRNA levels. These results should enhance our understanding of the clinical heterogeneity observed in the patients with iduronate sulfatase deficiency. Restriction fragment length polymorphism studies at the iduronate sulfatase gene locus should allow improved carrier detection in Hunter syndrome. The studies on the molecular genetics of iduronate sulfatase deficiencies will form the basis for future gene transfer studies in Hunter syndrome.