I am finally getting back to my canine health screening series. You can access previous posts in the series, here.
A Note About The Series
This series covers the various health screening tests that are available to breeders to assist them in making breeding decisions. When you purchase a purebred puppy you should expect that a reputable breeder has done health screenings on the parents of that dog. In fact, you should expect that health screenings have been done on several generations of the dogs in your puppy’s pedigree.
Keep in mind that while a particular health screening test may be recommended for a certain breed, if there is a low occurrence of that disease in a particular breed or in the lineage of particular dogs, the breeder may elect not to do it. A prospective breeding dog is more than any particular health screening. A better approach is to consider the entire dog, including health, proper temperament, conformation and important breed characteristics.
This post is about the eye disease PRA (Progressive Retinal Atrophy), specifically the type of PRA known as prcd-PRA which is a common form of PRA.
What is prcd-PRA?
prcd-PRA is an inherited eye disease that leads to blindness. “prcd” stands for “progressive rod-cone degeneration”. Dogs affected with prcd-PRA have normal vision when they are young, but as they age, the cells in the retina at the back of the eye degenerate and die and eventually they become blind. Generally the onset of the disease is around 5-7 years, although it can begin in adolescence or early adulthood in some breeds.
PRA cannot be treated so it must be prevented through informed breeding decisions.
How is prcd-PRA Inherited?
prcd-PRA is a single-gene simple recessive disease, which means dogs that are affected by this disease have inherited one mutated gene (which causes the disease) from each parent. I went into more detail about modes of genetic inheritance and DNA testing here.
Dogs can either be Normal/Clear, Carrier or Affected. Normal/Clear dogs do not carry the gene which causes this disease. Carrier dogs carry one normal gene and one gene which causes the disease, but they will not develop the disease. Affected dogs have two of the genes which cause the disease and they will eventually develop the disease.
If Normal/Clear dogs are bred to other Normal/Clear dogs, they will only produce Normal/Clear puppies, (none of the pups will inherit the gene which causes the disease). Carrier and Affected dogs must only be bred to Normal/Clears. At worst, this mating will produce puppies that are Carriers. Again, while Carriers carry the disease gene, they will not develop the disease. Carrier and Affected dogs should not be bred together because they will produce some Affected dogs.
How Do Breeders Screen For prcd-PRA?
Testing is done through a blood test or a buccal cheek swab. These are sent to a lab for DNA testing. Many breeders in the USA use OptiGen for PRA testing.
On their website, OptiGen lists the breeds for which the prcd-PRA test is available. You can access the list here. Keep in mind that research is always ongoing and they may develop tests for additional breeds in the future.
How Should Puppy Buyers Use This Information?
For Chesapeake Bay Retrievers this test is relatively new. The first tests just looked for markers that indicated the presence of the PRA gene. It was not until 2005 that a test was developed that identified the actual mutated gene.
Before testing was available, this was one of those particularly frustrating diseases because the sire and dam of a litter may not have been affected (in the case of two Carriers), yet they produced offspring that were. In addition, the onset of the disease did not always occur before the dogs had been bred (in the case of an Affected dog). Breeders had no reliable tool to assist them when making breeding decisions.
That is not the case today because breeders now have a reliable test. Anyone buying a purebred puppy should research whether their breed is affected by PRA and whether there is a screening test available. They should ask prospective breeders whether the parents of the pups have been tested and the results of the tests.
The next installment in the series will be on Exercised Induced Collapse. Hopefully I can keep a better schedule and post the next installment in a couple of weeks.
Sources:
Golden Retrievers are on the list, too; but so far, neither Callie nor Shadow appear to be affected at 10-1/2 and 10 years respectively. They do have “selective” hearing, though, just like their human grandfather and great-grandmothers. 🙂
It’s so reassuring that there are tests like this available. And yes I can see how terrible this would have been before the testing – not being able to predict when a dog will be effected because it can come from carriers. Thanks so much for the great information – it helps prospective puppy buyers so much more aware of all the health screening possibilities they need to ask about. Very helpful in determining whether a breeder is reputable or not; someone that cares enough for their reputation and breed to do the research and make responsible choices. Looking forward to exercise induced collapse; my Lab that we had growing up suffered from it and it was horrifying the first time it happened; I didn’t know what was wrong with him. Luckily our vet told us about the syndrome and we were able to monitor his activity levels after that.
Oooh, I’m glad you picked up this series again, I learn so much from it!! I have not heard of this disease but do see that Labradors are on that list. Since both my dogs are over the typical age when the disease is detected, I am guessing we are okay.
I love seeing the photos of the dogs when they were puppies. I see even then Storm had a thing for her Kong. 🙂
Oh, I never heard of that. Great idea to post about this so people can be informed. Folks need to do their homework before they get a new pup!
Great information, thank you for sharing this!
People really need to know what to ask when buying a purebred dog, so this is great information. It’s so encouraging to see that more and more tests are available to get the information needed.
Agree with Jan K. And thanks for picking up the series again. 🙂
Thanks for doing this series, very informative.