GUCY2D and retinal disorder: This presented a challenge because the main trigger for the photoreceptor degeneration in GUCY2D and GUCA1A retinopathies starts in the outer segment, where the mutant RetGC1:GCAP1 complex produces excess of cGMP in the dark, subsequently causing opening of the excessive number of cGMP gated channels, thus elevating free cGMP and Ca2+ in the outer segment (10, 11, 12).