What does this mean? Cornell University has developed a DNA gene test for prcd-PRA (Progressive Retinol Atrophy), which is an inherited eye disease that causes blindness. In order for a dog to develop prcd-PRA, it must have two prcd-PRA genes, one inherited from each parent. If it only gets one prcd-PRA gene, or none, it will most likely never develop prcd-PRA. Optigen is the lab which offers the test for the price of $195 per dog (ouch!), and claims "almost" 100% accuracy. Dogs can be tested at any age. The test results that come back from Optigen are labeled as Normal/Clear (previously Pattern A), Carrier (previously Pattern B) or Affected (previously Pattern C), and here is what Optigen says about those:
What does Normal/Clear (or Homozygous Normal) mean? This means the dog has no prcd-PRA gene, and therefore an extremely low risk of developing prcd-PRA. This dog can be safely bred to any other dog, even a dog with prcd-PRA, and none of the puppies will be affected with prcd-PRA.
What does Carrier (or Heterozygous) mean? This means the dog has only one prcd-PRA gene, and therefore an extremely low risk of developing prcd-PRA. If bred, this dog would have a 50/50 chance of passing its one prcd-PRA gene to its offspring. But remember, its other gene is normal, not prcd-PRA, so it also has a 50/50 chance of passing its normal gene to its offspring. Since a puppy would need two prcd-PRA genes, one from each parent, in order to develop prcd-PRA, this Carrier dog could be safely bred to a Normal/Clear dog and none of the puppies would develop prcd-PRA. Some of them might be Normal/Clear (statistically, 50%) and some of them might be Carriers (statistically, 50%), but none of them will be affected with prcd-PRA. If this Carrier dog is bred to another Carrier dog, however, there is a possibility of producing prcd-PRA Affected puppies (statistically, 25%), but there is also the same possibility of producing Normal/Clear puppies (again, statistically 25%). Some breeders might take this chance because there aren't very many Normal/Clear dogs to breed to right now. But if they can develop more of them by breeding two Carriers together, eventually we will have a lot more Normal/Clear dogs. If your breeder has bred two Carriers together, ask their reasons for doing so, and if you are satisfied with their answer, then you may wish to consider having your puppy Optigen tested.
So what about Affected (or Homozygous Mutant)? This means the dog has two prcd-PRA genes, and a very high chance of developing prcd-PRA sometime during its lifetime. Currently that is estimated to be anywhere from 3 to 13 years of age (or unknown actually). There are a few Eskies out there who are 8-10 years old, Optigen tested as Affected, and still not showing any symptoms of prcd-PRA. The good news about the Optigen test is that an Affected dog can be safely bred to a Normal/Clear dog and no Affected puppies will be produced, only Carriers. Which means, those puppies won't get prcd-PRA. Breeding an Affected dog to a Carrier, however, is not recommended because it would give the puppies a 50% chance of being prcd-PRA Affected themselves, and no chance of being Normal/Clear.
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