A clinical trial using autologous hematopoietic stem cell transplantation of CD34 cells corrected with lentiviral vector overexpressing human ARSA (HSCT-GT) has shown very encouraging results and provides strong evidence of clinical benefit in pre-symptomatic patients with late infantile MLD (LI-MLD) and pre or early symptomatic patients with early juvenile MLD (EJ-MLD; NCT015601821) (Biffi et al., 2013; Sessa et al., 2016). The gene discussed is CD34; the disease is metachromatic leukodystrophy.