In MLD mutations in the arylsulfatase A (ARSA) gene cause ARSA deficiency with subsequent accumulation of 3-sulfogalactocerebroside especially in oligodendrocytes.
Metachromatic leukodystrophy (MLD) is an autosomal-recessive lysosomal storage disease caused by mutations in the ARSA gene leading to arylsulfatase A (ARSA) deficiency and causing sulfatide accumulation.
Cellulose acetate gel electrophoresis of fibroblast extracts from the patient showed no detectable arylsulfatase A isozyme under conditions that clearly distinguished pseudo-arylsulfatase A deficiency from classical MLD.
Arylsulfatase A (ASA) is found to be deficient in healthy individuals (pseudo arylsulfatase A deficiency) who usually show in vitro ASA levels in the range of metachromatic leukodystrophy patients.
With both techniques, cultured fibroblasts from patients with pseudo-arylsulfatase A deficiency showed faint but clear bands of arylsulfatase A activity.
In conclusion, although pseudo arylsulfatase-A deficiency and metachromatic leukodystrophy have very different clinical outcomes, they are due to mutations of the same structural gene, coding for arylsulfatase-A.