Common Symptoms
Progressive retinal Atrophy, PRA1 (papillon type) is an adult-onset, inherited eye disease affecting phalenes. Progressive retinal atrophy, PRA1 (papillon type) occurs as a result of degeneration of the Rod type Photoreceptor Cells of the Retina, which are important for vision in low light. Affected dogs typically present between 4 to 6 years of age with poor vision in dim light. On a veterinary eye exam affected dogs have changes in reflectivity and appearance of a structure behind the retina called the Tapetum as well as thinning of the retinal blood vessels, signifying decreased blood flow to the retina. Progressive retinal atrophy, PRA1 (papillon type) is slowly progressive and some affected dogs maintain vision in daylight for many years, sometimes for the remainder of their life.
Breed-Specific Information for the Phalene
The Mutation of the CNGB1 gene associated with progressive retinal Atrophy, PRA1 (papillon type) has been identified in the phalene. Though the exact frequency in the overall phalene population is unknown, 17.2% out of 145 phalenes and the closely related papillon dog breed from a randomly selected population from Finland had one copy of the mutation and were therefore carriers of the mutation.
Testing Tips
Genetic testing of the CNGB1 gene in phalenes will reliably determine whether a dog is a genetic Carrier of progressive retinal Atrophy, PRA1 (papillon type). Progressive retinal atrophy, PRA1 (papillon 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 CNGB1 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. Phalenes 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 CNGB1 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.
References
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Ahonen SJ, Arumilli M, Lohi H. A CNGB1 frameshift mutation in Papillon and Phalène dogs with progressive retinal atrophy. PLoS One. 2013 Aug 28;8(8):e72122.
[PubMed: 24015210]
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Winkler PA, Ekenstedt KJ, Occelli LM, Frattaroli AV, Bartoe JT, Venta PJ, Petersen-Jones SM. A large animal model for CNGB1 autosomal recessive retinitis pigmentosa. PLoS One. 2013 Aug 19;8(8):e72229.
[PubMed: 23977260]
