While the reason for the retinal specificity of the phenotype is currently unclear there is ample precedent for isolated retinal degeneration occurring as a result of higher retinal requirements for widely expressed proteins, including components of the spliceosome (PRPF31 [24], PRPF8 [25], PRPF3 [1,26], SNRNP200 [27], PRPF6 [28], and PRPF4 [29],) and transcription factors (ZNF513) [30]. This evidence concerns the gene PRPF4 and retinal degeneration.