ABCA4 and Usher syndrome: While the allele frequency depends on the studied population, in aggregate, mutations in the ABCA4 gene (Stargardt disease), EYS (associated with non-syndromic RP, cone-rod dystrophy, and LCA), USH2A (associated with Usher syndrome, type 2, as well as non-syndromic RP), CEP290 (associated with LCA, type 10), and MYO7A (associated with Usher syndrome, type 1) account for more than one third of all cases of IRDs [7,18,19,20].