Beverley A. Pack

Lysosomal enzyme activities in fresh and frozen chorionic villi and in cultured trophoblasts

Fifteen lysosomal enzyme activities were compared in 14 presumed normal chorionic villus specimens that were each divided, processed and analyzed as fresh tissue, tissue frozen for 1 week, and cultures established from minced whole villi. Most of the activities determined in the chorionic villus tissue were not affected significantly by freezing. However, activities for most enzymes were significantly different from those determined in the cultured cells. Our experience with first trimester prenatal evaluations for several lysosomal disorders showed that the limited amount of tissue obtained is not always sufficient for thorough analysis and thus, cultured trophoblasts derived from the tissue specimen should also be examined. The results of this study stress the importance of using appropriate tissue-type and cell-type controls to establish the normal range in the respective analyses.

INCREASED SERUM HEXOSAMINIDASE A DURING PREGNANCY: IMPLICATIONS FOR TAY-SACHS CARRIER DETECTION BY SULFATED FLUOROGENIC SUBSTRATES

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 womens 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.