The abundance of loss-of-function mutations, including complete gene deletions, in PRPF31 patients has led to a consensus view that haploinsufficiency is the disease mechanism in this form of RP(Abu-Safieh et al., 2006; Rio Frio et al., 2008b; Rose and Bhattacharya, 2016). The gene discussed is PRPF31; the disease is retinitis pigmentosa 1.