ABCA4 and severe early-childhood-onset retinal dystrophy: Mutations in the ATP-binding cassette subfamily A member 4 gene (ABCA4, previously called ABCR, OMIM 601691) have been described as being responsible for a series of abnormalities, including cone-rod dystrophy 3 (CORD3, OMIM 604116), RP19 (OMIM 601718), age-related macular degeneration 2 (OMIM 153800), fundus flavimaculatus (FFM), Stargardt disease 1 (STGD1), and early-onset severe retinal dystrophy (OMIM 248200) [14–19].