ABCA4 and severe early-childhood-onset retinal dystrophy: Among these conditions, Stargardt disease (STGD1; MIM_248200) is the most common form of inherited macular degeneration and is caused by mutations in the ATP-binding cassette subfamily A member 4 gene (ABCA4; CDS: 6.8 kb),20 while Usher syndrome type 1B, a severe form of combined hearing loss and vision loss due to retinitis pigmentosa, is caused by mutations in the gene encoding for Myosin 7A (MYO7A; CDS: 6.6 kb).21