ABCA4 and severe early-childhood-onset retinal dystrophy: Thecorresponding gene, ABCA4, was cloned in 1997, and variantswere identified as the cause of autosomal recessive Stargardt disease (STGD1).Over the next two decades, variation in ABCA4 has beenattributed to phenotypes other than the classically defined STGD1 or fundusflavimaculatus, ranging from early onset and fast progressing cone-rod dystrophyand retinitis pigmentosa-like phenotypes to very late onset cases of mostly milddisease sometimes resembling, and confused with, age-related maculardegeneration.