Morquio B syndrome: a primary defect in beta-galactosidase.
Fibroblasts from patients with Morquio B syndrome contain normal numbers of beta-galactosidase molecules with normal turnover but strongly reduced activity per enzyme molecule. Various substrate affinities are abnormal: the Km for methylum belliferyl (MU)-beta-galactoside is 4-10-fold elevated and affinity for keratan sulphate and oligosaccharides, isolated from Morquio B urine, was not detectable. In contrast, these substrate affinities are normal for beta-galactosidase in adult type GM1-gangliosidosis fibroblasts. Cell hybridization studies demonstrate that Morquio B syndrome and infantile and adult type GM1-gangliosidosis belong to the same complementation group. From these results we conclude that Morquio B syndrome is caused by a mutation in the structural gene for beta-galactosidase, which is allelic to the mutations in infantile and adult type GM1-gangliosidosis. Urinary excretion of keratan sulphate and oligosaccharides is abnormal in Morquio B syndrome but normal in adult type GM1-gangliosidosis. The catalytic properties of beta-galactosidase in Morquio B syndrome and GM1-gangliosidosis provide a possible explanation for the distinct clinical manifestations in these disorders.
D005347:Fibroblasts / Q000201:enzymology; D005696:Galactosidases / Q000235:genetics*; D006025:Glycosaminoglycans / Q000652:urine; D006801:Humans; D006822:Hybrid Cells / Q000201:enzymology; D007787:Lactose Intolerance; D009085:Mucopolysaccharidosis IV / Q000201:enzymology* / Q000235:genetics / Q000652:urine; D009154:Mutation; D009439:Neuraminidase / Q000378:metabolism; D009844:Oligosaccharides / Q000652:urine; D001616:beta-Galactosidase / Q000235:genetics*
D006025:Glycosaminoglycans; D009844:Oligosaccharides; D005696:Galactosidases; D009439:Neuraminidase; D001616:beta-Galactosidase