Rod-cone dysplasia in Irish setters: a defect in cyclic GMP metabolism in visual cells.

An abnormality in retinal guanosine 3,5-monophosphate (cyclic GMP) metabolism is demonstrated in the inherited rod-cone dysplasis of Irish Setter dogs. Affected visual cells are deficient in cyclic GMP phosphodiesterase activity and have elevated levels of cyclic GMP. The biochemical abnormalities observed in affected retinas of Irish Setters are similar to those in the retinas of mice with inherited retinal degeneration before visual cell degeneration begins. A defect in cyclic GMP metabolism may be characteristic of early-onset degenerative diseases of the retina, possibly including those that affect humans.