Treatment of MLD characterized by biallelic mutations in the ARSA gene leading to a reduction of the ARSA enzymatic activity: in children with late infantile or early juvenile forms, without clinical manifestations of the disease, and in children with the early juvenile form and with early clinical manifestations of the disease, who still have the ability to walk independently and before the onset of cognitive decline. This evidence concerns the gene ARSA and metachromatic leukodystrophy.