Increased expression of β-hexosaminidase α chain in cultured skin fibroblasts from patients with carbohydrate-deficient glycoprotein syndrome type I

Carbohydrate-deficient glycoprotein (CDG) syndrome type I is an autosomal recessive multisystem disorder characterized by multiple serum glycoproteins with deficient oligosaccharide chains. This characteristic under-glycosylation is found in several serum glycoproteins. We studied secreted forms of lysosomal enzymes, β-hexosaminidase and α-fucosidase, in serum from the patients and media of cultured fibroblasts. Both β-hexosaminidase and α-fucosidase activities were increased in sera from three CDG patients. The enzyme activity staining using the fluorogenic substrate-4-methylumbelliferyl-α- -fucopyranoside after polyacrylamide gel isoelectric focusing revealed abnormal cathodal bands in sera from CDG patients. On the other hand, no abnormal secreted forms of β-hexosaminidase and α-fucosidase were detected in media from cultured CDG fibroblasts by isoelectric focusing and sodium-dodecyl sulfate-polyacrylamide gel electrophoresis. However, SDS-polyacrylamide gel electrophoresis and Western blotting analysis of β-hexosaminidase using anti-β-hexosaminidase A (anti-α+β chains) antibody, showed an increase of a 55-kDa mature form of the α chain. Northern blotting analysis identified an increase in mRNA levels of β-hexosaminidase α chain in CDG fibroblasts. Although under-glycosylated fractions of these lysosomal enzymes were not detected in cultured fibroblasts, it was suggested that intracellular processing of these lysosomal enzymes in CDG patients might be altered.