Abstract
Carrier detection of Tay-Sachs disease (TSD) in sera is unreliable during pregnancy when based on the heat inactivation method. This is due to an increase in the relatively thermostable serum hexosaminidase (Hex) P, and is overcome by testing leukocytes. Since sulfated fluorogenic substrates (MUβGIcNAc-6-S & MUβGa1NAc-6-S) are highly specific for Hex A and provide direct determination independent of heat-labile/heat-stable ratio, we have examined their value in TSD carrier detection in pregnant women's sera. Determination of Hex activity toward sulfated substrates was carried out in isolated isozyme fractions from sera, leukocytes and fibroblasts of controls, pregnant TSD carriers and non-carriers, and TSD and Sandhoff disease patients. The results indicated that the cleavage en bloc of the N-acetylhexosamine-6-sulfate is catalyzed by an active site on the α-subunit, since only negligible activity was associated with Hex isozymes B, I1, I2 and P, and Hex S (α2) was twice as active as Hex A (αβaβb). The results also indicated that in addition to serum Hex P there is an increase in serum Hex A which starts during the second trimester of pregnancy. We conclude that accurate TSD carrier detection in serum during pregnancy may be possible if gestational age-matched controls are used.
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