title: Residual α-L-iduronidase activity in fibroblasts of mild to severe Mucopolysaccharidosis type I patients.
abstract: Three major clinical subgroups are usually distinguished in Mucopolysaccharidosis type I: Hurler (MPS IH, severe presentation), Hurler-Scheie (MPS IH/S, intermediate) and Scheie (MPS IS, mild). To facilitate treatment with hematopoietic stem-cell transplantation, early diagnosis is important for MPS IH patients. Although screening for MPS I in newborns would allow detection at an early age, it may be difficult to predict the phenotype on the basis of the genotype in these infants. Extra diagnostic tools are thus required. Based on the hypothesis that distinct MPS I phenotypes may result from differences in residual α-l-iduronidase (IDUA) activity, we modified the common IDUA assay using the substrate 4-methylumbelliferyl-α-l-iduronide to allow quantification of low IDUA activity in MPS I fibroblasts. Enzyme incubation was performed with high protein concentrations at different time points up to 8h. Mean residual IDUA activity was 0.18% (range 0-0.6) of the control value in MPS IH fibroblasts (n=5); against 0.27% (range 0.2-0.3) in MPS IH/S cells (n=3); and 0.79% (range 0.3-1.8) in MPS IS fibroblasts (n=5). These results suggest that residual IDUA activity and severity of the MPS I phenotype are correlated. Two MPS IS patients with rare (E276K/E276K) or indefinite (A327P/unknown) IDUA genotypes had residual IDUA activity in the MPS IS range, illustrating the usefulness of our approach. IDUA(E276K) was very unstable at 37°C, but more stable at 23°C, suggesting thermal instability. We conclude that this procedure for determining residual IDUA activity in fibroblasts of MPS I patients may be helpful to predict MPS I phenotype.
authors.affiliation: Department of Pediatrics, Center for Lysosomal and Metabolic Diseases, Erasmus Medical Center, Rotterdam, The Netherlands. e.oussoren@erasmusmc.nl
authors.forename: Esmee
authors.initials: E
authors.lastname: Oussoren
authors.forename: Joke
authors.initials: J
authors.lastname: Keulemans
authors.forename: Otto P
authors.initials: OP
authors.lastname: van Diggelen
authors.forename: Linda F
authors.initials: LF
authors.lastname: Oemardien
authors.forename: Remco G
authors.initials: RG
authors.lastname: Timmermans
authors.forename: Ans T
authors.initials: AT
authors.lastname: van der Ploeg
authors.forename: George J G
authors.initials: GJ
authors.lastname: Ruijter
mesh_terms: D002460:Cell Line; D042241:Early Diagnosis; D005347:Fibroblasts / Q000201:enzymology*; D006801:Humans; D006923:Hymecromone / Q000031:analogs & derivatives* / Q000378:metabolism; D007068:Iduronidase / Q000378:metabolism*; D007231:Infant, Newborn; D008059:Mucopolysaccharidosis I / Q000175:diagnosis* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D009154:Mutation
chemical_list: D006923:Hymecromone; C018343:4-methylumbelliferyl iduronide; D007068:Iduronidase
keywords: 4-methylumbelliferone; 4MU; ERT; HSCT; Hurler; Hurler syndrome; Hurler–Scheie syndrome; IDUA; MPS; MPS IH; MPS IH/S; MPS IS; Mucopolysaccharidosis; Newborn screening; Residual activity; Scheie; Scheie syndrome; enzyme-replacement therapy; hematopoietic stem cell transplantation; mucopolysaccharidosis; α-l-iduronidase