Investigations of micro-organic brain damage (MOBD) in heterozygotes of metachromatic leukodystrophy.

Potential damage of central and peripheral nervous system expressed as micro-organic brain damage (MOBD) was investigated in 27 unrelated heterozygotes with metachromatic leukodystrophy (MLD). Arylsulfatase A (ARSA) was determined in peripheral blood leukocytes and sulfatide excretion was estimated in 24-hour urine collections. Genomic DNA was analyzed for the ARSA pseudodeficiency (PD) allele by a PCR method. Clinical investigations included examination of hyper-reflexia, Babinski reflex, Wechsler Adult Intelligence Scale, Benton test, evoked potentials, and nerve conduction velocity (NCV). In our study, a higher incidence of evident or possible micro-organic brain damage was observed in true MLD/PD and MLD heterozygotes (NO/MLD, where NO means the wild allele) than in controls. On the basis of the Benton test, MOBD was suggested or indicated in 67% of MLD heterozygotes, 50% of MLD/PD heterozygotes, and 26% of controls. In our small group of carriers with MLD and PD mutations, persons NO/MLD(PD) with one wild-type allele did not show MOBD and displayed higher ARSA/beta-galactosidase ratios, unlike true MLD/PD compound heterozygotes who carry MLD-causing mutation in one allele and the ARSA-PD polymorphism in the second. Theoretically, this is a shift from autosomal recessive to autosomal dominant-like inheritance, especially when one cannot exclude the influence of polymorphisms (like ARSA-PD) in the wild allele. Since all psychological tests were age-matched, it can be assumed that the MOBD observed in MLD carriers does not have a progressive character unlike in MLD patients. However, it should be mentioned that MOBD appears to have no overt clinical consequences.