Progressive Retinal Atrophy (Irish Setter Type)

Common Symptoms

Progressive retinal Atrophy (Irish setter type) is an early onset, inherited eye disease affecting Irish setters. Progressive retinal atrophy (Irish setter type) occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. The rod type cells are affected first and dogs present around 1 month of age with vision deficits in dim light (night blindness) and loss of peripheral vision. By 5 months of age dogs have complete loss of night vision and also show visual deficits in bright light. Other signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the retina called the Tapetum that can be observed on a veterinary eye exam. Although there is individual variation in disease progression, generally the disease follows a rapid progression and dogs are typically completely blind by 1 year of age.

Breed-Specific Information for the Irish Setter

The Mutation of the PDE6B gene associated with progressive retinal Atrophy (Irish setter type) has been identified in the Irish setter. Though the exact frequency in the overall Irish setter population is unknown, 7.8% out of 436 Irish setters from a population from the US, 0.5% of 210 Irish setters from the UK and none of the 38 Irish setters tested from Australia were carriers of the mutation.

Testing Tips

Genetic testing of the PDE6B gene in Irish setters will reliably determine whether a dog is a genetic Carrier of progressive retinal Atrophy (Irish setter type). Progressive retinal atrophy (Irish setter type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the PDE6B gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Irish setters that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of progressive retinal atrophy (PRA) caused by mutations in other genes, a normal result in PDE6B does not exclude PRA in a pedigree.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.

References

• Aguirre GD, Baldwin V, Weeks KM, Acland GM, Ray K. Frequency of the codon 807 Mutation in the cGMP phosphodiesterase beta-subunit gene in Irish Setters and other dog breeds with hereditary retinal degeneration. J Hered. 1999 Jan-Feb;90(1):143-7. [PubMed: 9987922]
• Maroudas P, Jobling AI, Augusteyn RC. Genetic screening for progressive retinal atrophy in the Australin population of Irish Setters. Aust Vet J. 2000 Nov;78(11):773-4. [PubMed: 11194724]
• Petersen-Jones SM, Clements PJM, Barnett KC, Sargan DR. Incidence of the gene mutation causal for rod-cone dysplasia type 1 in Irish setters in the UK. J Small Anim Pract. 1995 Jul;36(7):310-4. [PubMed: 7474961]
• Suber ML, Pittler SJ, Qin N, Wright GC, Holcombe V, Lee RH, Craft CM, Lolley RN, Baehr W, Hurwitz RL. Irish setter dogs affected with rod/cone dysplasia contain a nonsense mutation in the rod cGMP phosphodiesterase beta-subunit gene. Proc Natl Acad Sci U S A. 1993 May 1; 90(9):3968-72. [PubMed: 8387203]