Progressive retinal Atrophy, Rod-cone dysplasia 2 is an early-onset, inherited eye disease affecting rough collies. Progressive retinal atrophy, rod-cone dysplasia 2 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. Affected dogs have abnormal thinning and degeneration of the retina beginning around 16 days of age. The rod type cells are affected first and affected dogs will initially have vision deficits in dim light (night blindness) and loss of peripheral vision noticeable at about 6 weeks of age. 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 at 3.5-4 months of age on a veterinary eye exam. As the disease progresses, cone photoreceptor cells also degenerate resulting in complete blindness by 6 to 8 months of age.
Breed-Specific Information for the Rough Collie
The Mutation of the RD3 gene associated with progressive retinal Atrophy, Rod-cone dysplasia 2 has been identified in rough collies, although its overall frequency in this breed is unknown.
Genetic testing of the RD3 gene will reliably determine whether a rough collie is a genetic Carrier of progressive retinal Atrophy, Rod-cone dysplasia 2. Progressive retinal atrophy, rod-cone dysplasia 2 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 being a carrier of the RD3 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. Rough collies that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of PRA caused by mutations in other genes, a normal result in RD3 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.
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