Although this phenotype is highly selective and affects primarily rod photoreceptors, a substantial fraction of RP- cases have been linked to mutations in the general splicing factors PRPF3, PRPF4, PRPF6, PRPF8, PRPF31 and SNRNP200 [9]–[14]. Here, PRPF4 is linked to retinitis pigmentosa 1.