Progressive retinal Atrophy, cone-Rod dystrophy 2 is an early-onset inherited eye disease affecting dogs. The disease affects the Photoreceptor Cells of the Retina and results in the progressive loss of vision. Affected dogs typically have abnormal thinning and degeneration of the retina by 12 weeks of age. Evidence of retinal thinning can be identified on a veterinary eye exam by 3 to 6 months of age. Vision is severely impaired by one year of age and by 20 months of age affected dogs have an advanced stage of retinal degeneration.
Genetic testing of the IQCB1 gene will reliably determine whether a dog is a genetic Carrier of progressive retinal Atrophy, cone-Rod dystrophy 2. Progressive retinal atrophy, cone-rod dystrophy 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 inheriting one copy and being a carrier of the IQCB1 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. 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 IQCB1 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.
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Kijas JW, Zangerl B, Miller B, Nelson J, Kirkness EF, Aguirre GD, Acland GM. Cloning of the canine ABCA4 gene and evaluation in canine cone-rod dystrophies and progressive retinal atrophies. Mol Vis. 2004 Mar 29;10:223-32.