MLD diagnosis was confirmed by severely reduced arylsulfatase A activity (0,7 nmol/h/mg) (ref. 3.5–15 nmol/h/mg) and identification of homozygosity for the previously described pathogenic c.1277C>T; p.(P426L) variant in the ARSA gene. This evidence concerns the gene ARSA and metachromatic leukodystrophy.