Variation of arylsulphatase A: comparative studies of arylsulphatase A with synthetic and natural substrates in three families with metachromatic leucodystrophy.

Arylsulphatase A activity was measured in leucocytes and cultured tibroblasts from individuals of three families with late infantile and adult metachromatic leucodystrophy, comparing enzyme assays with natural and two synthetic substrates including a simple and sensitive test employing 4-methylumbelliferly sulphate and AgNO3. Enzyme activities were compared with those obtained after isoelectric focusing. Arylsulphatase A values obtained for different heterozygotes were almost continuously scattered over the entire range from patient level to normal level. Nevertheless arylsulphatase A values of the heterozygotes were at least sligtly higher than the activity of diseases persons when measured with three different assays. The possibility is discussed of a crucial minimal level of residual arylsulphatase A activity necessary to avoid manifestation of the disease.