ABCA4 and severe early-childhood-onset retinal dystrophy: The mutant variants in ABCA4 are mainly responsible for autosomal recessive retinal dystrophies, including Stargardt disease (STGD1; OMIM 248200) [1, 7], retinitis pigmentosa (RP19; OMIM 601718) [8, 9], cone-rod dystrophy (CRD3; OMIM 604116) [10, 11], and early-onset severe retinal dystrophy (OMIM 248200) [12, 13].