title: A novel mucopolysaccharidosis type I associated splice site mutation and IDUA splice variants.
abstract: Mucopolysaccharidosis type I is an autosomal recessive disorder caused by deficiency of α-l-iduronidase, encoded by the IDUA gene. More than 100 disease causing mutations have been reported in the gene, resulting in a wide range of phenotypes. Here we describe a previously unreported IDUA splice site mutation (NG_008103.1:g.21632G>C; NM_000203.3:c.1727+3G>C) causing a Hurler phenotype in a patient heterozygous for the common p.Q70X (NG_008103.1:g.5862C>T) mutation. Sequence analysis of IDUA transcripts demonstrated that the g.21632G>C mutation results in aberrant splicing of intron 12 (NM_000203.3:c.1727_1728insGTCC), introducing a frame shift and premature termination codon (NP_000194.2:p.Cys577SerfsX15). Gene expression studies suggest that the deleterious effect of the mutation is primarily due to a C-terminal truncation of the encoded polypeptide. Furthermore, we observed that both normal and mutant IDUA alleles give rise to alternatively spliced transcripts in leukocytes. Exclusion of exon 4 appeared to be the predominant alternative splicing event, probably resulting in polypeptides lacking iduronidase activity. The Hurler patient demonstrated exon 4 skipping in 5.6% of IDUA transcripts, while exon 4 skipping ranged 25-34% of transcripts among healthy individuals (n=5). Alternative splicing might represent a mechanism for regulation of this enzyme, and the lower level of exon 4 skipping in the patient might be a response to intracellular accumulation of iduronidase substrates. Molecular characterization of IDUA mutations and splicing may assist early prediction of mucopolysaccharidosis type I phenotypes and increase the understanding of disease mechanisms. This is important considering the choice of current treatment options and for the development of future therapies.
authors.affiliation: Department of Medical Biochemistry, Oslo University Hospital, PO Box 4950 Nydalen, N-0424 Oslo, Norway. sara.bremer@oslo-universitetssykehus.no
authors.forename: Sara
authors.initials: S
authors.lastname: Bremer
authors.forename: Annika
authors.initials: A
authors.lastname: Ohlsson
authors.forename: Else
authors.initials: E
authors.lastname: Brodtkorb
authors.forename: Helge
authors.initials: H
authors.lastname: Rootwelt
authors.forename: Terje
authors.initials: T
authors.lastname: Rootwelt
authors.forename: Berit
authors.initials: B
authors.lastname: Woldseth
authors.forename: Lars
authors.initials: L
authors.lastname: Mørkrid
mesh_terms: D017398:Alternative Splicing / Q000235:genetics*; D001483:Base Sequence; D018389:Codon, Nonsense / Q000235:genetics; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics; D005260:Female; D016368:Frameshift Mutation / Q000235:genetics; D040461:Gene Components; D006025:Glycosaminoglycans / Q000652:urine; D006801:Humans; D007068:Iduronidase / Q000235:genetics*; D007223:Infant; D008969:Molecular Sequence Data; D008059:Mucopolysaccharidosis I / Q000235:genetics* / Q000473:pathology; D009664:Norway; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D020033:Protein Isoforms / Q000235:genetics*
chemical_list: D018389:Codon, Nonsense; D006025:Glycosaminoglycans; D020033:Protein Isoforms; D007068:Iduronidase