Detection of homozygotes and heterozygotes for metachromatic leukodystrophy in lymphoid cell lines and peripheral leukocytes.

Assays of arylsulphatase A have been performed on peripheral leukocytes and lymphoid cell lines from normal subjects and heterozygotes and homozygotes for metachromatic leukodystrophy (MLD) by utilizing an improved procedure based on the removal of excess protein from the final digest. No overlap of arylsulphatase A activity was observed between peripheral leukocytes obtained from 11 normal donors, 8 heterozygotes and 5 homozygotes for MLD. Absence of enzyme activity was demonstrated in the patients' leukocytes, when the modified assay procedure was employed. Arylsulphatase A activity (mean +/- S.D.) in 30 lymphoid lines and sublines established from 18 normal donors, 2 heterozygotes and 1 homozygote for MLD was 54-5 +/- 23-1, 24-1 +/- 3-2 and 0-9, respectively. The enzymic activity of arylsulphatase A and B remained stable over a period of several months. These findings indicate that long-term lymphoid lines express the genotype of the donor and maintain enzyme stability over long periods in culture. Moreover, it appears that peripheral leukocytes are a reliable system for the identification of the carrier state of MLD.