Prenatal Diagnosis of Metachromatic Leukodystrophy in a Family with Pseudo Arylsulfatase A Deficiency by the Cerebroside Sulfate Loading Test

Abstract

Summary: Prenatal diagnosis was requested by a family at risk for metachromatic leukodystrophy (MLD). An examination of the family leukocyte arylsulfatase A profile revealed that the mother had pseudo arylsulfatase A deficiency. Cultured amniotic fluid cells were deficient in arylsulfatase A, so two possibilities were indicated: the fetus was affected with MLD or had the pseudodeficiency phenotype. The only known biochemical test to differentiate the two enzyme deficient phenotypes is cerebroside sulfate loading of growing fibroblasts. The pseudodeficient cells hydrolyze the incorporated sulfatide as efficiently as control cells, whereas MLD cells show no hydrolysis. Application of this test to the at risk cultured amniotic fluid cells resulted in appreciable uptake of the sulfolipid, but no hydrolysis. Control amniotic fluid cell cultures hydrolyzed 82 to 95% of the incorporated sulfatide. Therefore, an affected fetus was indicated. Fibroblasts derived from the aborted fetus showed a deficiency of arylsulfatase A and a similar inability to hydrolyze cerebroside sulfate in the loading test. The loading technique allowed the prenatal diagnosis of MLD when the arylsulfatase A analysis was equivocal. Speculation: In metachromatic leukodystrophy families with pseudo arylsulfatase A deficiency, the usual enzyme assays on cultured amniotic fluid cell extracts fail to differentiate between the fetus with the affected phenotype and the fetus with the pseudodeflciency phenotype. The cerebroside sulfate loading test in growing cultured amniotic fluid cells allowed this discrimination. It is important to examine the family enzyme profile for the pseudodeficiency phenotype as a prerequisite hi the prenatal diagnosis of metachromatic leukodystrophy to avoid the erroneous identification of a pseudo-deficient fetus as a metachromatic leukodystrophy fetus.