Wahlin et al. (2013) first reported aberrant DNA methylation levels in the rd1 mouse model of retinitis pigmentosa (RP), a widely used model that displays rapid rod photoreceptor loss that peaks between postnatal days 12–14 (P12-14; for a summary of all preclinical models discussed in this review, refer to Supplementary Table S1) (Keeler, 1924; LaVail and Sidman, 1974; Portera-Cailliau et al., 1994; Wahlin et al., 2013). The gene discussed is PDE6B; the disease is retinitis pigmentosa 1.