title: Hurler syndrome: a patient with abnormally high levels of alpha-L-iduronidase protein.
abstract: Mucopolysaccharidosis type I (MPS I: McKusick 25280) is a clinically heterogenous lysosomal storage disorder which is caused by a variable deficiency in alpha-L-iduronidase activity (alpha-L-iduronide iduronohydrolase, EC 3.2.1.76). Cultured fibroblasts from an MPS I patient (cell line 2827) with a severe clinical phenotype (Hurler syndrome) have been characterized using immunochemical and biochemical techniques. Using a specific immunoquantification assay, we have demonstrated that cell line 2827 had an alpha-L-iduronidase protein content (189 ng/mg of extracted cell protein) at least six times greater than the mean level found in normal control fibroblasts (30 ng/mg of extracted cell protein). This was the only MPS I cell line, from a group of 23 MPS I patients, that contained greater than 7% of the mean level of alpha-L-iduronidase protein detected in normal controls. Cell line 2827 had very low alpha-L-iduronidase activity toward the fluorogenic substrate 4-methylumbelliferyl-alpha-L-iduronide, and a radiolabeled disaccharide substrate derived from heparin. Maturation studies of alpha-L-iduronidase in cell line 2827 showed apparently normal levels of alpha-L-iduronidase synthesis with delayed processing to the mature form. Subcellular fractionation experiments demonstrated alpha-L-iduronidase protein in lysosomal-enriched fractions isolated from cell line 2827, suggesting a normal cell distribution and supporting the proposed delayed processing. It is proposed that the MPS I patient described has an alpha-L-iduronidase gene mutation which affects both the active site and post-translational processing of the enzyme. This mutation must be structurally conservative because it does not result in instability either during maturation or in the lysosome.
authors.affiliation: Department of Chemical Pathology, Adelaide Children's Hospital, South Australia.
authors.forename: D A
authors.initials: DA
authors.lastname: Brooks
authors.forename: G S
authors.initials: GS
authors.lastname: Harper
authors.forename: G J
authors.initials: GJ
authors.lastname: Gibson
authors.forename: L J
authors.initials: LJ
authors.lastname: Ashton
authors.forename: J A
authors.initials: JA
authors.lastname: Taylor
authors.forename: P A
authors.initials: PA
authors.lastname: McCourt
authors.forename: C
authors.initials: C
authors.lastname: Freeman
authors.forename: P R
authors.initials: PR
authors.lastname: Clements
authors.forename: J W
authors.initials: JW
authors.lastname: Hoffmann
authors.forename: J J
authors.initials: JJ
authors.lastname: Hopwood
mesh_terms: D002478:Cells, Cultured; D002675:Child, Preschool; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007068:Iduronidase / Q000032:analysis*; D008247:Lysosomes / Q000201:enzymology; D008297:Male; D008059:Mucopolysaccharidosis I / Q000378:metabolism*; D011506:Proteins / Q000032:analysis*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D011506:Proteins; D007068:Iduronidase