Initially, the siblings were reported to have an atypical form of metachromatic leukodystrophy (MLD) on the basis of markedly reduced levels of arylsulfatase A in fibroblasts and leucocytes, reduced nerve conduction velocities, and the detection of brown metachromatic granules in sural nerve biopsies. The gene discussed is ARSA; the disease is metachromatic leukodystrophy.