GUCA1A encodes guanylate cyclase-activating protein 1 (GCAP1), a calcium-sensitive regulator of retinal guanylyl cyclase critical for photoreceptor function. GCAP1 stimulates guanylyl cyclase when intracellular calcium is low and inhibits it when calcium rises, enabling recovery of the dark state in rod photoreceptors following light exposure 1234. This calcium-dependent regulation of cyclic GMP levels is essential for normal phototransduction 5. GUCA1A mutations cause autosomal dominant cone dystrophy 3 (COD3) and cone-rod dystrophy 14, characterized by progressive central vision loss and color vision defects typically onset in the third to fifth decade 67. Disease pathology involves altered rather than loss of GCAP1 function; mouse models carrying disease mutations show abnormal cGMP accumulation preceding photoreceptor degeneration, with cone dysfunction predominating over rod involvement 8. Clinical presentations show substantial intrafamilial heterogeneity, with specific variants conferring different severity profiles: p.(Tyr99Cys) is most common, while p.(Glu111Ala) associates with worse vision and p.(Leu84Phe) with earlier-onset disease 7. Electrophysiology typically reveals cone dystrophy patterns with variable rod involvement 9. GUCA1A variants account for a small proportion of inherited retinal disease cases 1011.