Based on previous animal studies (36, 37) and the clinical cases describing loss of function in RetGC1 associated with a recessive blindness, GUCY2D Leber’s congenital amaurosis (38, 39, 40), RetGC1 is the main isozyme of RetGC providing most of cGMP production in mammalian photoreceptors, including human rods and cones. Here, GUCY2D is linked to blindness (disorder).