GUCY2D and cone-rod dystrophy 6: Gain‐of‐function mutations in retinal guanylate cyclase 2D (GUCY2D), which encodes retinal guanylate cyclase 1 (RetGC1), are the leading cause of cone‐rod dystrophy 6 (CORD6) with the loss of early‐onset cone cell and central/color vision [193].