ARSA and metachromatic leukodystrophy: Metachromatic leukodystrophy (MLD, MIM #250100) is a neurometabolic disorder caused by biallelic disease‐causing variants in ARSA (MIM*607574), resulting in deficiency of the lysosomal enzyme arylsulfatase A (ASA) and subsequent (lyso)sulfatides accumulation in the peripheral and central nervous system [1].