First, ASA endocytosis and routing to the lysosomes is mediated by a mannose-6-phosphate receptor-dependent mechanism.26 However, ASA secreted by macrophages and microglia was shown to lack mannose-6-phosphate, hampering its uptake by recipient cells.27 In a postmortem study involving 2 patients with MLD treated with HSCT who died from disease progression, ASA was identified in donor macrophages in the CNS, in a granular lysosomal pattern, confirming presence of ASA in the CNS after transplantation. Here, ARSA is linked to metachromatic leukodystrophy.