Although to date more than twenty mutations in the gene GUCA1A encoding for GCAP1 have been associated with autosomal dominant cone dystrophy or cone–rod dystrophy (28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39), only one relatively rare missense mutation substituting Gly157 for an arginine (indicated from now on with G157R) has been found in GUCA1B encoding for GCAP2 in Japanese families with a history of retinitis pigmentosa, in some cases with macular involvement (40, 41). This evidence concerns the gene GUCA1A and retinitis pigmentosa.