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

Abstract

SummaryPrenatal 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 arylsdfatase 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 sbowed a deficiency of arylsulfatase A and a similar inability to hydrolyze cerebroside sulfate i n the loading test. The loading technique allowed the prenatal diagnosis of MLD when the arylsulfatase A analysis was equivocal. Speculation I n 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 pseudodeficiency phenotype. The cerebroside sulfate loading test in growing cultured amniotic fluid cells allowed this discrimination. I t is important to examine the family enzyme profile for the peudodeficiency phenotype as a prerequisite in the prenatal diagnosis of metachromatic leukodystrophy to avoid the erroneous identification of a pseudodeficient fetus as a metachromatic leukodystrophy fetus.In metachromatic leukodystrophy (MLD), the profound deficiency of arylsulfatase A (ajlsuifaie ~ulfohydrola&, EC 3.1.6.1) leads to the accumulation of cerebroside sulfate in neural tissue ~ resulting in progressive neurological degeneration (5). Based on the age of onset of symptoms, three classical types of MLD are recognized: late infantile, juvenile, and adult. Each type appears to be an independent autosomal recessive disorder, so allelism is implied. Although no treatment is available, the disorder can be prevented in at risk families because MLD is amenable to prenatal diagnosis. In affected pregnancies, cultured amniotic fluid cells are deficient in arylsulfatase A (10,14,17,(21)(22)(23)(24).Dubois el al. (3, 4). Lott el al. (15). and Fluharty el al. (8) described four MLD families in which one of the parents and some of the unaffected children had very low arylsulfatase A activities which overlapped the range of probands. These individuals showed no neurologic dysfunction and were healthy, so it would be appropriate to iypifi the apparent enzyme deficikncy as a ~seudodeficiencv. The attenuated enzyme activity was observed in' leukocyte anda fibroblast extracts khether thk ...

Diagnosis of Metachromatic Leukodystrophy, Krabbe Disease, and Farber Disease after Uptake of Fatty Acid-labeled Cerebroside Sulfate into Cultured Skin Fibroblasts

“…The assays in vitro may require high concentration of bile salts or other additives to activate the enzyme in question. In recent years false positive or pseudode-ficient carriers (low enzyme activity in vitro in a healthy person) of MLD (4)(5)(6)(7)(8)(9) and Krabbe disease (10) have been reported. These families present a problem when prenatal diagnosis for the disease in question is requested.…”

Cholesterol Ester and Triglyceride Metabolism in Intact Fibroblasts from Patients with Wolman's Disease and Cholesterol Ester Storage Disease

“…In addition, these investigators were able to correlate the clinical phenotypes with the levels of residual activity observed in the intact cell. Similarly, studies of cerebroside sulfate hydrolysis in intact fibroblasts have been useful in differentiating between metachromatic leukodystrophy and the benign pseudo arylsulfatase A deficiency, both of which are associated with very low levels of arylsulfatase A and cerebroside sulfatase activity in cell lysates (9,13).…”

Pseudo arylsulfatase A deficiency Biosynthesis of an abnormal arylsulfatase A

“…In addition to the relatively greater stability of the mutant ARA molecules in PD, the 5-10070 of residual ARA activity in PD cells demonstrated catalytic activity towards both artificial [12] and natural substrates for ARA [13]. In contrast, the residual activity in MLD cells did not possess similar activity.…”