Mutations in the mouse ortholog of NR2E3 have been identified in the spontaneous mutant retinal degeneration 7 (rd7) [15]. This mutant demonstrates slow retinal degeneration and abnormal lamination of the ONL with rosette formation [15,16]. Curiously, the ERG of the mouse under both light and dark adaptation has been reported to be normal, showing progressive attenuation with time, presumably due to degenerative cell loss [15]. A prior study showed a 2- to 3-fold increase in the number S-opsin–positive cells in the rd7 retina compared to wild type [17]. In addition, two groups recently reported derepression of additional cone genes in the rd7 mutant [18,19].