ABCA4 and Usher syndrome: To provide proof of principle for CATALYTEC, we initially focused on the IRD genes ABCA4, RPE65, MYO7A, and USH2A for several reasons: (a) These genes are frequently mutated in the corresponding diseases: ABCA4, Stargardt disease (STGD1); RPE65, Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP); USH2A, RP and Usher syndrome (USH).