Molecular basis of mucopolysaccharidosis type VII: replacement of Ala619 in beta-glucuronidase with Val

Abstract

We have identified a mutation causing beta-glucuronidase (beta Gl) deficiency in a 6-year-old girl with mucopolysaccharidosis type VII. Enzyme assay of lysates of a girl's lymphocytes or cultured fibroblasts showed little residual activity and a normal beta Gl-specific mRNA level, as revealed by Northern-blot analysis. Sequencing of the full-length mutated cDNA revealed a C----T transition, an event causing a single Ala619----Val change (we designated this variant beta GGifu). This change is detected by loss of the cleavage site for the enzyme Fnu4HI in the mutated cDNA. On the basis of the loss of Fnu4HI restriction site, the patient was shown to be a homozygote with the beta GGifu mutation and her parents and brother were heterozygotes. This mutation disrupts a functional domain consisting of a region of sequence highly conserved among human, rat and bacterial beta Gls, and it reduces the enzyme activity, as tested by transfection of COS cells with expression vectors harboring the mutated cDNA.