RPE65 and severe early-childhood-onset retinal dystrophy: The discovery of the underlying genetic causes over the last two decades has led to far greater understanding of disease mechanisms in IRD which has informed development of novel therapies, culminating in the first gene therapy trials for RPE65-associated Leber congenital amaurosis (LCA)/Early Onset Severe Retinal Dystrophy (EOSRD) in 2008.2–4