Unlike the mutations detected in LCA, which are mainly located in the catalytic and kinase-like domains of the RetGC-1 [7,8], most of the mutations identified in COD or CORD are located in the putative dimerization domain, which extends from amino acid 817 to 857 [2-5,12-15,17,18,22,23]. The gene discussed is GUCY2D; the disease is Leber congenital amaurosis.