PRA-rcd1 in Irish Setters

PRA-rcd1 (rod-cone dysplasia) is a form of progressive retinal atrophy (PRA) with early onset of the disease. This specific form of PRA affects Irish Setter dogs.

PRA-rcd1 is hereditary eye defect. Photoreceptor degeneration starts in two weeks of age. Degeneration is completed by about 1 year when affected dog is totally blind.

PRa-rcd1 disease is caused by nonsense mutation G>A in codon 807 of PDE6B gene (gene for β-subunit cGMP phosphodiesterase enzyme (PDE)). This mutation forms premature stopcodon; the mutated enzyme is 49 amino acids shorter (C-terminal domain is missing) and cannot fulfill its normal function. So, cGMP levels in retina are markedly elevated.

PRA-rcd1 disease is incurable but it can be preceded. Genetic test can reveal normal individuals, carrier individuals or affected individuals. On the basis, a breeding program can be compiled to rcd1 defect excluding.

PRA-rcd1 is autosomal recessive inherited disease. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive / negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

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References:

Parry HB (1953), Br. J. Ophthal. 37, 487-502

Aguirre G, Faber D, Lolley R, Obrien PO, Alligood J, Fletcher RT, Chader G (1982), Exp. Eye Res. 35, 625-642

Suber ML, Pittler SJ, Qin N, Wright GC, Holcombre V, Lee RH, Craft CM, Lolley RN, Baehr W, Hurwitz RL: Irish setter dogs affected with rod/cone dysplasia contain a nonsence muitation in the rod cGMP phosphodiesterase ß-subunit gene, Proc. Natl. Acad. Sci. USA, 90, 3968-3972 (1993)