The prenatal diagnosis of Tay-Sachs disease.

Tay-Sachs disease was diagnosed prenatally on the basis of enzyme assays and the electrophoretic pattern of extracts made from cultured amniotic fluid cells. Electrophoresis revealed the presence of hexosaminidase B but no hexosaminidase A, the iso-enzyme which is deficient in Tay-Sachs disease. Estimations of the percentage of hexosaminidase A present in cultured amniotic cell extracts by means of thermal fractionation revealed the presence of only small amounts of this isozyme. Results obtained on amniotic fluid alone were found to be unreliable and were disregarded when making the diagnosis. Following termination of the pregnancy, the diagnosis was confirmed by electrophoresis and the thermal inactivation method as well as by electron microscopy. A slight lower temperature for the thermal inactivation has been found to give better discrimination than the temperature used in previously described techniques.