Despite the differences in the actual molecular events that affect Ca2+ sensitivity of the cGMP production between GUCY2D and GCAP1 dominant retinopathies, previous studies demonstrated that in both cases deregulation of cGMP production in the dark is the primary trigger for degeneration of photoreceptors harboring mutant RetGC1 or GCAP1 in living photoreceptors (11, 12, 13). This evidence concerns the gene GUCY2D and retinal disorder.