Specifically, the use of gene transfer to boost the production of the Arylsulfatase A (ARSA) enzyme in HSPC-derived myeloid progeny is key to ensure a therapeutic advantage in MLD patients (Biffi et al., 2013; Sessa et al., 2016), in line with the results of pre-clinical studies in MLD mice (Biffi et al., 2006). This evidence concerns the gene ARSA and metachromatic leukodystrophy.