Abstract
Total serum hexosaminidase activity is generally measured quantitatively by the amount of fluorescent product formed by action of its various isoenzymes on the 4-methyl-umbelliferyl-β-D-N-acetylglucosaminide substrate at pH 4.5. Only the heat labile form of the enzyme (Hex A) is inactive in fluids and tissues of Tay-Sachs children. Known carriers (parents) have serum Hex A values about sol1 2 of those found for non-carriers. Carrier detection tests, presently utilized for the mass screening of the Ashkenazi Jewish population, are based either on prolonged heat inactivation or electrophoretic separation of Hex A from its other serum isoenzymes. We found that serum Hex A can also be inactivated by 5 min incubation at pH 2.8 ± 0.05 and 37°. This finding led to a simple, rapid, quantitative assay for Hex A which was applied to 29 sera (14 normal, 8 carrier, 4 pregnancy and 3 Tay-Sachs disease). Except for the pregnancy and carrier groups, there was no overlap in serum Hex A values for any of the other categories. The results by acid pH inactivation correlated well with those obtained by the heat denaturation procedure. The greater potential of the acid inactivation method for automated systems, suitable for mass screening of carriers, is presently under development.
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