PRDM1 and retinitis pigmentosa: NRL mutations have been associated with retinitis pigmentosa (Bessant et al., 1999) and mutations in Blimp-1, RORβ, Otx2, Crx, or Nrl are associated with a loss of rod PRs in mammals (Mears et al., 2001; Nishida et al., 2003; Daniele et al., 2005; Koike et al., 2007; Jia et al., 2009; Katoh et al., 2010).