GUCY2D and Leber congenital amaurosis 12: RD3 deficiency reduces RetGC content in the photoreceptor outer segment and suppresses retinal photoresponses (1, 15), making rods and cones dysfunctional from birth in recessive human Leber’s congenital amaurosis-12 (LCA12) (1, 16) and rd3 mouse strain (1).