Two abnormalities of hexosaminidase A in clinically normal individuals.

Two abnormalities of beta-hexosaminidase A (HEX A) activity are described. One, found in two unrelated Jewish children, was characterized by the complete absence of HEX A activity in serum, but low levels of activity in leukocytes and fibroblasts using artificial substrate. The other, found in a non-Jewish man, was characterized by uniformly low levels of HEX A activity in leukocytes, fibroblasts, and serum against artificial substrate. In all cases, the pH optimum of HEX A was normal, there was no increased lability at 37 degrees C, and no inhibitor was detected to account for the deficiency of activity. Cultured fibroblasts of these individuals were capable of synthesizing and processing alpha- and beta-subunits of HEX A and capable of cleaving GM2 ganglioside. The patients, ranging in age from 6 to 30 years, are clinically normal. They are probably genetic compounds carrying the classical Tay-Sachs gene and a differently mutated allele that imparts the anomalous phenotypic features observed.