We have previously described the kinetics of association of the alpha- and beta-subunits of beta-hexosaminidase A in intact cultured human fibroblasts, using biosynthetic labeling and immunoprecipitation with antisera that distinguish between monomeric and associated alpha-chains (Proia, R. L., d'Azzo, A., and Neufeld, E. F. (1984) J. Biol. Chem. 259, 3350-3354). We now show lack of alpha-beta association in fibroblasts of several individuals deficient in beta-hexosaminidase A (5 patients with nonclassic forms of Tay-Sachs disease and 2 asymptomatic siblings). Defective association was accompanied by markedly reduced (less than one-tenth of normal) conversion of the alpha-chain precursor of Mr = 67,000 to the mature lysosomal form of Mr = 54,000. Analysis by hybridization with fibroblasts lacking the alpha- or beta-chain showed that the association defect resided in the alpha-chain. Most of the cell strains studied also had decreased synthesis of the alpha-chain, suggesting compound heterozygosity with the Ashkenazi Tay-Sachs (no synthesis) allele. An unusual feature of the association defect is the variability in the resulting clinical manifestations, even within families, implying that other factors determine the adequacy of the residual associated beta-hexosaminidase A in vivo.

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