ARSA and metachromatic leukodystrophy: Furthermore, the first clinical trial of autologous HSC transplantation with lentivirally transduced, “supertherapeutic” ARSA gene expression in pre-symptomatic children with arylsulfatase A (ARSA) deficiency (the cause of metachromatic leukodystrophy) was recently completed, and appears to have been successful at preventing the demyelination associated with sulfatide accumulation for at least two years post-therapy [92,93].