Metachromatic leukodystrophy (MLD) is a progressive, autosomal recessive neurodegenerative disorder caused by mutations in the arylsulfatase A (ARSA) gene, which result in a deficiency of the lysosomal enzyme ARSA and the pathological accumulation of sulfatides in cells (1–3). Here, ARSA is linked to metachromatic leukodystrophy.