Low levels of β hexosaminidase A in healthy individuals with apparent deficiency of this enzyme

Appreciable β hexosaminidase A (hex A) activity was detected in cultured skin fibroblasts and melanoma tissue from healthy individuals previously reported as having deficiency of hex A activity indistinguishable from that of patients with Tay Sachs disease (TSD). Identification and quantitation of hex A, amounting to 3.5%-6.9% of total β hexosaminidase activity, has been obtained by cellulose acetate gel electrophoresis, DEAE cellulose ion exchange chromatography, radial immunodiffusion, and radioimmunoassay. Previous family studies suggested that these individuals may be compound heterozygotes for the common mutant TSD gene and a rare (allelic) mutant gene. Thus, the postulated rare mutant gene appears to code for the expression of low amounts of hex A. Heterozygotes for the rare mutant may be indistinguishable from heterozygotes for the common TSD mutant. However, direct visualization and quantitation of hex A by the methods described may prevent false positive prenatal diagnosis of TSD in fetuses having the incomplete hex A deficiency of the type described in the 4 healthy individuals.