Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by an arylsulfatase A deficiency. It is one of the sphingolipidoses, as the enzyme deficiency leads to an accumulation of the sphingolipid cerebroside sulfate. Metachromatic leukodystrophy is also categorized as a leukodystrophy, meaning that there is degeneration in the brain's white matter. This occurs secondary to abnormal myelination, which again is caused by a build-up of cerebroside sulfate and its metabolites. Patients with metachromatic leukodystrophy present with neurologic dysfunction, notably dementia and ataxia.