Among them, Lenmeldy is based on ARSA gene delivery for the treatment of metachromatic leukodystrophy (MLD); Skysona on transferring adrenoleukodystrophy protein (ALDP) encoded by the ABCD1 gene to treat cerebral adrenoleukodystrophy (CALD); and Lyfgenia and Zynteglo for the treatment of both sickle cell disease and β-thalassemia by providing functional copies of a modified βA-globin gene, respectively [37]. The gene discussed is ABCD1; the disease is sickle cell disease.