Prenatal diagnosis of Sanfilippo A syndrome: experience in 35 pregnancies at risk and the use of a new fluorogenic substrate for the heparin sulphamidase assay.

We have investigated the use of a 4-methylumbelliferone (MU)-derived artificial substrate, MU-alpha-D-N-sulphoglucosaminide, for the sulphamidase assay in chorionic villi and amniotic fluid cells. In the new two-step enzyme assay, fluorescent MU is released by the successive action of endogenous sulphamidase and an added yeast enzyme preparation which hydrolyses the MU-alpha-glucosaminide intermediate. Optimal conditions for a sensitive, accurate, and convenient procedure for use in the prenatal diagnosis of Sanfilippo A syndrome are described. Previously, prenatal diagnosis of Sanfilippo A syndrome has been achieved by a radioactive sulphamidase assay in chorionic villi or in cultured amniocytes and by two-dimensional electrophoresis of glycosaminoglycans in amniotic fluid. Our experience using these methods in 35 pregnancies at risk is reported. The feasibility of the new fluorogenic assay was evaluated by retrospective testing of stored homogenates of chorionic villi and amniotic fluid cells from 22 pregnancies at risk. Unequivocal assignment of the fetal status in five affected pregnancies and 17 pregnancies with a normal outcome confirms the reliability of the new sulphamidase assay, which is in every respect more convenient than the conventional method using 35S-radiolabelled heparin.