Rod/cone dysplasia 1 (rcd1 Progressive Retinal Atrophy) observed in the Irish Setter breed, is an autosomal recessive trait leading to progressive loss of photoreceptors. While rod photoreceptor degeneration is evident by 1 month of age, vision loss is typically completed by about 1 year of age. Rcd1 is caused by a nonsense mutation in the cGMP phosphodiesterase gene ( G - A transition converting TGG to TAG at codon 807 of the protein). This mutation creates a premature stop codon that truncates the PDE6???? protein, which is required for posttranslational processing and membrane association.