Despite the considerable genetic heterogeneity in RP pathogenesis, investigation of specific RP-associated genes has yielded important insights into critical visual cycle-associated proteins as well as structural and metabolic proteins involved in rod photoreceptor development and function, including rhodopsin [17], RPE65 (expressed in retinal pigmented epithelium and supports phototransduction) [18], RPGR [19] and NRL/NR2E3 [20,21]. Here, NRL is linked to retinitis pigmentosa 1.