GUCY2D and Leber congenital amaurosis: Mutations in GUCY2D (encoding photoreceptor-specific retinal guanylate cyclase-1) are associated with recessive Leber congenital amaurosis-1 (LCA1) in humans (13,37), and GC1/GC2 double KO (dKO) mice exhibit rapid photoreceptor degeneration, diminished ERG responses, and abnormal OS morphology (38), all phenotypes consistent with the morphological defects observed in Reep6 KO mice.