Alpha-L-Iduronidase Deficiency in Mucopolysaccharidosis Type I Against a Radiolabelled Sulfated Disaccharide Substrate Derived from Dermatan Sulfate

alpha-L-Iduronidase activity was assayed by incubation of a radiolabelled disaccharide, O-(alpha-L-idopyranosyluronic acid)-(1----3)-2,5 anhydro-D-[1,3H]-talitol 4-sulfate (IdoA-anT4S) derived from dermatan sulfate, with homogenates of leucocytes, cultured amniotic cells and skin fibroblasts from normal individuals and patients affected with an alpha-L-iduronidase-deficiency disorder (mucopolysaccharidosis type I, MPS I), parents of such patients and patients affected with other mucopolysaccharidoses. The assay clearly distinguished affected homozygotes from normal controls, heterozygotes and other mucopolysaccharidosis types. Preliminary results show that fibroblast homogenates from patients with the MPS I Hurler phenotype were virtually unable to hydrolyse IdoA-anT4S, whereas fibroblast homogenates from a patient with a relatively mild (Scheie) phenotype exhibited a residual activity with Vmax value of 2.5 pmol/min/mg protein and an apparent Km of 21 mumol/l compared to a range of 1020-2105 pmol/min/mg for Vmax and 12-35 mumol/l for Km for fibroblasts from normal controls.