Generalized Progressive Retinal Atrophy is an adult-onset inherited eye disease affecting dogs. Generalized progressive retinal atrophy occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, important for vision in dim light and daylight, respectively. Initial clinical 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. Affected dogs initially present between 2 and 5 years of age with vision loss in dim light (night blindness) and loss of peripheral vision, gradually progressing to complete vision loss. The disease follows a variable progression and severity depending on the individual and complete
Genetic testing of the CCDC66 gene will reliably determine whether a dog is a genetic Carrier of generalized progressive retinal Atrophy. Generalized progressive retinal atrophy 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 CCDC66 gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms do not appear until adulthood, genetic testing should be performed before breeding. 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. Dogs that are not found to have this specific mutation have no increased risk of having affected pups. However, because there are multiple types of progressive retinal atrophy caused by mutations in other genes, a normal result in CCDC66 does not exclude progressive retinal atrophy 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.
Dekomien G, Vollrath C, Petrasch-Parwez E, Boeve MH, Akkad DA, Gerding WM, Epplen JT. Progressive retinal atrophy in schapendoes dogs: mutation of the newly identified CCDC66 gene. Neurogenetics. 2010 May;11(2):163-74.
Lippmann T, Jonkisz A, Dobosz T, Petrasch-Parwez E, Epplen JT, Dekomien G. Haplotype-defined linkage region for gPRA in schapendoes dogs. Mol Vis. 2007 Feb 7;13:174-80.