Enzyme immunoassay of beta-hexosaminidase A and B in serum: carrier detection of GM2-gangliosidoses, and equivalence of enzyme activity and enzyme protein reactivity.

beta-Hexosaminidase (Hex; EC 3.2.1.52) isoenzymes A and B were analyzed in sera from a control group of 22 apparently healthy subjects, 13 obligate carriers of Tay-Sachs disease (TSD), 10 obligate carriers of Sandhoff disease (SHD), and 4 affected TSD patients by enzyme immunoassay methods based on enzyme activity. No Hex A activity was detected in the sera of patients with TSD. The activities of Hex A in the obligate carriers of TSD and SHD tended to be lower (nonsignificantly) than in the control group. Hex B activities tended to be higher in TSD patients as well as in carriers of TSD, although the mean activities did not significantly differ from the corresponding mean for the control group. However, Hex B activities were decreased in the carriers of SHD in comparison with the other groups. Sera from 900 postmenopausal women, all of age 55 years, were also analyzed for Hex isoenzymes; the results indicated a carrier frequency of about 1 in 200 for both TSD and SHD. We also compared the enzyme immunoassay method based on enzyme activity with one based on the antigenic (enzyme protein) reactivity alone. Because both methods yielded similar information, we conclude that no significant amounts of inactive enzyme protein are present in the circulation.