GUCA1A and Macular dystrophy: The guanylate cyclase activator 1A gene (GUCA1A), located in 6p21.1, encodes guanylyl cyclase-activating protein 1 (GCAP1), and has been identified as being involved in dominant cone dystrophy, cone-rod dystrophy and macular dystrophy (Payne et al., 1998; Wilkie et al., 2000).