Adeno-associated virus (AAV)-mediated gene therapy has shown promising efficacy in several in vivo or in vitro BCD models.12–15 In particular, the recombinant AAV2/8–human CYP4V2 (rAAV-hCYP4V2) vector, which produces the functional wild-type human CYP4V2 protein (patent no. CN113106124B), has been found to be efficient in an induced pluripotent stem cells-derived RPE from a patient with BCD as well as in a Cyp4v3-knockout mouse model,14 providing the basis for a clinical trial for this gene therapy. The gene discussed is CYP4V2; the disease is Bietti crystalline corneoretinal dystrophy.