Metachromatic leukodystrophy (MLD) is a lysosornal storage disorder caused by deficiency in arylsulfatase A (ASA). Concentrations of cholesterol and its metabolites were determined in ASA deficient [ASA(-/-)] mice which serve as an animal model of MLD. We observed a significant reduction in cholesterol content in the brain of adult ASA(-/-) mice when compared to wild-type controls. This was not due to loss of myelin, because ASA(-/-) mice do not demyelinate. Other cholesterol metabolites were not changed significantly in ASA(-/-) mice, except for an increase in lathosterol. Moreover, reduced cholesterol levels were also found in tissue samples from two juvenile MILD cases. Since high cholesterol levels are important for myelination, and various cellular processes, like vesicular trafficking and signal transduction, reduced cholesterol levels might be an important factor in the molecular pathology of MILD. (c) 2006 Elsevier Inc, All rights reserved.