GUCY2D and Leber congenital amaurosis: For example, it cannot be excluded33 that, in SNB patients, in contrast to LCA patients, cGMP regulation in L- and M-cones (less frequently in S-cones), but not in rods, for some reason becomes partially compensated by the second isozyme of RetGC, RetGC2 (GUCY2F), which usually presents a minor component in cGMP production.26