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Two children in a family with five siblings were investigated because of low levels of fibroblast arylsulfatase A activity. Neither child had metachromatic leukodystrophy (MLD) and they were diagnosed as having benign pseudo arylsulfatase A deficiency trait (PD). Analysis of arylsulfatase A subunit profiles in fibroblasts provided data for genotype assignments for each family member. Father and mother were assigned an n/pd and n/mld phenotype, respectively. The low enzyme siblings were both assigned pd/mld; two of the three normal enzyme siblings were assigned an n/n phenotype and one an n/mld.

Low arylsulfatase A levels are reported in two siblings, one with a neurologic disability not typical for metachromatic leukodystrophy, the other a healthy 18-year-old female with a normal developmental history. In both individuals, arylsulfatase A levels in white blood cells were 7-8% of control values. Cultured fibroblasts gave low values (8-10% of normal) for both cerebroside sulfatase and arylsulfatase A activities. Other family members had enzyme levels consistent with heterozygote or normal status. Cerebroside sulfate loading tests of cultured fibroblasts in 199-CO2 media were normal for all family members who were tested. In MEM-HEPES media, however, cells from the two arylsulfatase A deficient siblings showed attenuated sulfolipid catabolism. Additional clinical and laboratory studies on these individuals failed to demonstrate any features suggestive of metachromatic leukodystrophy, i.e., normal nerve conduction velocities, normal sural nerve biopsy results, and normal urinary sulfatide excretion. It is concluded that the neurologic abnormalities in the one sibling are not the result of the low enzyme activity and that both individuals represent examples of pseudo arylsulfatase A deficiency (arylsulfatase A deficiency without metachromatic leukodystrophy). These results thus call into question the ability of the high-sensitivity cerebroside sulfate loading test as carried out in MEM-HEPES media to differentiate pathologically significant defects i.e., metachromatic leukodystrophy from benign "pseudo-deficiencies."

Deficient arylsulfatase A activity in man has long been associated with the neurodegenerative disease, metachromatic leukodystrophy. However, similar deficiency has been noted in clinically normal individuals, and is referred to as the pseudoarylsulfatase A deficiency condition. Although direct quantitative analysis of arylsulfatase A activity failed to differentiate between these two conditions, analysis of residual arylsulfatase A activity with either Cellogel electrophoresis or isoelectric focusing in polyacrylamide gels now has been shown to distinguish between them unequivocally. With both techniques, cultured fibroblasts from patients with pseudo-arylsulfatase A deficiency showed faint but clear bands of arylsulfatase A activity. Under identical conditions, fibroblasts from patients with metachromatic leukodystrophy showed no trace of activity. These methods can be adapted easily for general laboratory analysis in cases when results from quantitative arylsulfatase A assays are noninformative.

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.

Electrophoretic examination of extracts of cultured amniotic fluid cells from a pregnancy at risk for metachromatic leukodystrophy (MLD) showed absence of arylsulfatase A (AS-A) activity. Immunodiffusion with anti-human AS-A immune serum failed to show enzymatically active arcs of immune precipitate. Electrophoretic studies and quantitative assay of extracts of organs from the aborted fetus confirmed the diagnosis of MLD. Electrophoresis of amniotic fluid from this and one additional fetus with MLD showed an arylsulfatase pattern qualitatively and quantitatively indistinguishable from normal. In both normal and MLD fluids, the AS-A band was replaced by a band with lower anodal mobility. Only the anodal band of normal amniotic fluid, however, reacted with the anti-AS-A immune serum in immunoelectrophoresis. Assay of amniotic fluic with p-nitrocatechol sulfate (PNCS) as a substrate showed marked deficiency of "AS-A" activity in the fluids from the two MLD pregnancies. An optimal procedure for prenatal detection of MLD should include electrophoresis of extracts of cultured amniotic fluid cells with visual demonstration of absence of AS-A activity. Immunologic techniques applied to cell-free amniotic fluid may be of help in the rapid identification of the fetal genotypes.