title: alpha-L-iduronidase premature stop codons and potential read-through in mucopolysaccharidosis type I patients.
abstract: alpha-L-Iduronidase is a glycosyl hydrolase involved in the sequential degradation of the glycosaminoglycans heparan sulphate and dermatan sulphate. A deficiency in alpha-L-iduronidase results in the lysosomal accumulation and urinary secretion of partially degraded glycosaminoglycans and is the cause of the lysosomal storage disorder mucopolysaccharidosis type I (MPS I; Hurler and Scheie syndromes; McKusick 25280). The premature stop codons Q70X and W402X are two of the most common alpha-l-iduronidase gene (IDUA) mutations accounting for up to 70% of MPS I disease alleles in some populations. Here, we have reported a new mutation, making a total of 15 different mutations that can cause premature IDUA stop codons and have investigated the biochemistry of these mutations. Natural stop codon read-through was dependent on the fidelity of the codon when evaluated at Q70X and W402X in CHO-K1 cells, but the three possible stop codons TAA, TAG and TGA, had different effects on mRNA stability and this effect was context dependent. In CHO-K1 cells expressing the Q70X and W402X mutations, the level of gentamicin-enhanced stop codon read-through was slightly less than the increment in activity caused by a lower fidelity stop codon. In this system, gentamicin had more effect on read-through for the TAA and TGA stop codons when compared to the TAG stop codon. In an MPS I patient study, premature TGA stop codons were associated with a slightly attenuated clinical phenotype, when compared to classical Hurler syndrome (e.g. W402X/W402X and Q70X/Q70X genotypes with TAG stop codons). Natural read-through of premature stop codons is a potential explanation for variable clinical phenotype in MPS I patients. Enhanced stop codon read-through is a potential treatment strategy for a large sub-group of MPS I patients.
authors.affiliation: Academic Department of Medical Genetics, The Children's Hospital, Westmead, Australia.
authors.forename: Leanne K
authors.initials: LK
authors.lastname: Hein
authors.forename: Michael
authors.initials: M
authors.lastname: Bawden
authors.forename: Vivienne J
authors.initials: VJ
authors.lastname: Muller
authors.forename: David
authors.initials: D
authors.lastname: Sillence
authors.forename: John J
authors.initials: JJ
authors.lastname: Hopwood
authors.forename: Doug A
authors.initials: DA
authors.lastname: Brooks
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016466:CHO Cells; D018389:Codon, Nonsense; D006224:Cricetinae; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D007068:Iduronidase / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D008059:Mucopolysaccharidosis I / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D018389:Codon, Nonsense; D005839:Gentamicins; D012333:RNA, Messenger; D007068:Iduronidase