Frequently Asked Questions: pra
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3. Why does OptiGen NOT certify pups classified as Normal by Parentage?
Theoretically, it would be correct to expect all descendents from a normal x normal mating to be normal for that exact genetic disease. This is true if both parents in EVERY mating are known to be genetically normal either by genetic testing or by "normal by parentage".
However, in order to confidently rely on this approach, you need to consider the requirements and risks:
Our recommendation to concerned breeders is to always test the dogs that will be bred. You can rely more on "normal by parentage" for pets or dogs that won't be bred. If pets or non-breeders are carriers, they won't have the disease.
Based on all these reasons, OptiGen does not issue certificates for "normal by parentage."
- You must start out testing all of your breeding stock and any new breeding stock brought into your kennel. You must not rely on anyone's "word" that a dog is normal.
- You must confirm parentage relationships for every descendent on an ongoing basis through parentage analysis. There is a very real rate of mistakenly identified parents, typically sires. We must stress to you that cases of faulty parentage happen to the very best of breeders. Accidents happen. Double matings happen. You can rely on "normal by parentage" only if you document actual parentage. Some breed clubs and registering organizations consider ongoing risk of non-parentage high enough to justify acceptance of only one generation of "normal by parentage."
- You must accept that there is a very low, but real rate of inaccuracy in parentage testing. Sometimes, more than one male can be considered the potential sire because their DNA is so similar. Sometimes, mistakes are made.
- Regarding PRA, we believe there is more than one form of inherited PRA in some breeds. While the prcd form of PRA (detected by OptiGen's test) is by far the cause of the majority of PRA cases, a small portion remains unidentified. There's nothing we can offer at present, but you need to be aware that a second type of PRA could show up.
- The frequency of new mutations causing an inherited disease is extremely rare, but this risk really can't be factored in for practical purposes.
- And finally, if a human error were made anywhere along the line - samples labeled incorrectly, dogs identified incorrectly, a lab or office error was made, several generations could pass before the error was recognized. Great attention to detail at every step is required.
4. What do breeders ask OptiGen?
Most of the responses that follow were written by Mary M. Woodsen, a canine health writer. She reviewed queries coming to OptiGen about prcd-PRA testing. Then she talked with OptiGen scientists to get the information she needed for answers. These Q and A's were made into an article published in the ECSCA Review Winter 2000 and in the Labrador Quarterly Spring 2000.
5. Cataract Surgery - Should I consider cataract surgery for my PRA-affected dog? Should my dog get an ERG before deciding on cataract surgery to assess if there is good retina behind the cataracts?
In the past, conventional wisdom was a dog with PRA was not a candidate for cataract surgery, because its retina would not be capable of useful vision even if the cataract surgery were technically successful. This assumed two premises, which were generally accepted as true at the time. First, cataract surgery should be delayed until the cataracts were mature, and the dog was essentially blind from the cataracts. Second, complications from surgery were frequent, and success rates were "modest." However, things have changed. Success rates are higher, complication rates are lower, and the restoration of vision is better. So, a dog with PRA may in fact be a good candidate for such surgery. The decision for surgery comes down to cost vs. benefit. It could be argued that a dog with a late onset, slowly progressive form of PRA, such as prcd, and with a cataract interfering with central vision, should be considered for cataract surgery in order to best preserve whatever vision it has for as long as possible. Whether this makes financial sense is a decision for the owner. An ERG, done in a reliable fashion by an expert, will provide more information for making a fully informed cost/benefit decision regarding surgery. If the fundus (retina seen at the back of the eye) is visible, then an ERG should not be necessary. But if the fundus is not visible because the cataract is mature, then a good ERG can be useful. Overall, the best approach is to get annual CERF exams for your dog, so that a definitive diagnosis of cataract will be made before the cataract has progressed to the point of obscuring vision. Then, if surgery is considered, doing it before the cataract is mature is most helpful.
6. What is PRA? Is there any way to treat it? Can I prevent it?
Progressive Retinal Atrophy (PRA--and specifically, the prcd form of PRA) is an inherited eye disease rooted deep in the gene pool of at least a couple dozen breeds. Dogs with prcd-PRA often become blind, and always have serious vision problems.
In most breeds prcd-PRA manifests by the time a dog is at least six years old, after it has already been bred. However, in English Cocker Spaniels, prcd-PRA manifests even later, not until usually a dog is at least 8 years old. In order to develop PRA, a dog must inherit two copies of the defective prcd-PRA gene: one from its dam, one from its sire. Two recessive mutated genes equals disease in anyone's book--and there's no cure, no treatment; no way to stop it.
You can, however, prevent PRA in the next generation even though you can't treat it in the current generation. How? Through safe, selective breeding based on genetic testing.
7. Why is a prcd-PRA genetic test useful to me?
The test lets you identify normal dogs clear of the disease gene so you can better plan breeding strategies. It tells the status of an individual dog and gives a more accurate assessment of the risk of developing PRA, and eliminates the need for future ERGs in those dogs whose tests come back Normal/Clear or Carrier.
8. OptiGen uses a marker-based genetic test for prcd-PRA, but I heard it isn't always accurate as to whether a dog is clear or not. Why do you do this?
As announced June 1, 2005, OptiGen now provides a direct mutation test for prcd-PRA. The marker test has been retired.
9. Explain, please, what an allele is.
Alleles (say it a-lee-el) are different versions of the same gene. Does your sister have brown eyes, your brother hazel eyes, but yours are blue? In humans, eye color is caused by different alleles of the "eye-color gene." (Eye color is a bit more complex in dogs.) In the same way, genes for retinal functioning have different forms, or alleles...and the defective gene is one.
10. Do animals need to be tattooed or microchipped in order to have the test?
To be tested by OptiGen, dogs do not need to have permanent identification. However, there are situations where permanent ID is needed.
1. Permanent ID is needed for many registries; if you wish to have your dog entered in a registry, please make sure that you are providing all the information required by that registry.
2. In order to receive OptiGen’s special litter rate for multiple samples, puppies must have either a microchip or tattoo to “prevent mistaken identity” whether accidental or deliberate. Microchips can be inserted in 8-week-old pups (see "How old must my dog be to have a genetic test?")
11. How accurate is a direct mutation test?
The OptiGen direct mutation tests are exactly accurate. This means that the test gives clear readings in the laboratory; there is no issue of interpreting what we see. Numerous controls--absolute measures of accuracy--are used with every sample we process. The results for each dog will never change with age and will be the same whenever the same version of the test is repeated.
12. Is there any way a "Normal" dog could be PRA affected?
First, remember that PRA – Progressive Retinal Atrophy – is a broad category of disease that includes several types of retinal degenerative disease. One of these is prcd – progressive rod-cone degeneration. Prcd-PRA is the predominant type - by far - in many breeds currently being OptiGen tested. The OptiGen prcd-PRA mutation test detects only the prcd form of PRA and none other. Other specific forms of inherited PRA are detected in various breeds. Please refer to the link to "Tests".
Second, remember that a diagnosis of vision loss could be due to various causes. Maybe some type of known inherited PRA. Or maybe another type of PRA not yet testable. Or maybe a condition that isn’t a primary retinal problem at all, for example a secondary degeneration of the retina caused by a non-genetic disease. Even vision loss due to cataracts or detached retina is sometimes confused with PRA. Accurate diagnosis by a qualified specialist is extremely important.
Although only one type of PRA is known in some breeds, other breeds have one predominant form of PRA, as well as one or more unusual type(s) that don’t fit the clinical description or genetic profile of the predominant form.
13. CERF numbers show a very low frequency of PRA in the tested breeds but OptiGen numbers show an apparently higher incidence of probable affecteds. How do you compare the numbers?
Think for a minute about the difference between a radio poll and a professional Gallup Poll. The radio poll invites listeners to "call in and tell us your opinion." Both CERF and OptiGen results are sort of like that radio poll--you "call in" if you feel like it, and only the people in "calling distance," as it were, are likely to answer.
Gathering statistics for a Gallup Poll is a science in itself. It's not easy to estimate the true frequency of any specific thing, be it disease, gene, opinion, or behavior. Statisticians go to great (and expensive) lengths to preclude any bias in counting or reporting. Sampling must be random, must not exclude any groups or classes of information, must not have a tendency to count some groups (or classes of information) more than others, must be large enough to be significant, must not rely on volunteered information, and so on.
Neither CERF nor OptiGen is set up to generate such an unbiased population survey that could define the frequency of PRA in any breed. Both CERF and OptiGen simply offer the voluntary opportunity to register or to test. Granted, each of these sets of numbers does indicate something. But they're similar to snapshots, which show just a portion of the landscape, just one tree in the forest. The numbers have to be seen in context.
14. So, what's the context for CERF? What's the end result with CERF data?
For CERF, it's this: CERF records are not required on all registered dogs.
The CERF forms are used by the veterinary ophthalmologist when the owner chooses to request and pay for a CERF exam.
CERF counts one report form per dog per year, and dogs must be re-CERFed annually.
Clearly, a dog that CERFs normal is likely to be re-CERFed in following years. These dogs will be part of the numbers year after year. In contrast, the dog that fails a CERF exam probably will not be re-examined for CERF registration--it already failed. That dog's standing is included in the count for one year only, but not year after year. Not only that--but a dog that has already been diagnosed with an eye problem likely won't be given a CERF exam at all. (Note that the general eye exam form used by ACVO's does not go to
CERF, so many diagnoses are not registered. Only the specific CERF forms go to CERF.)
CERF numbers significantly underestimate the frequency of PRA and other inherited eye diseases in any breed.
15. And the context for OptiGen? What's the end result with OptiGen data?
OptiGen PRA testing is voluntary and new.
Its numbers are still small and come from a selected group of owners and dogs.
Some kennels are represented more than others.
Those owners testing first could represent a varied sampling of breeders, could be those who know or suspect their dogs are at risk, or a combination of both. We can't say for sure.
Owners usually do not test dogs that they already know are affected. They may well test the ones they think may be at risk.
Owners may test many related dogs--or even only related dogs. If those dogs have false alleles and are related through a line, they could be over-represented in our numbers.
Bottom line--OptiGen's sampling of tested dogs is not random. Any use of OptiGen test results as estimates of gene frequencies is not precise.
Neither CERF nor OptiGen numbers provide a reliable estimate of PRA in any breed.
CERF and OptiGen numbers are apples and oranges: they can't be statistically compared.
The OptiGen test is not designed to yield--and cannot effectively yield--a "frequency estimate" of PRA affecteds or carriers. It is designed to allow breeders to make informed decisions about how to prevent PRA in the pups they breed, and it does this with reliability.
16. Should I continue to CERF my dog?
Yes. The test for PRA does not provide information about other eye diseases that your dog may develop.
17. Why not just stick with ERGs for finding normal dogs?
Not every ERG exam is done reliably. To establish PRA-affected status by ERG, be sure that a full diagnostic protocol be done with dogs under anesthesia or heavy sedation; the rod and cone contributions of the ERG be separately evaluated.
Accurate ERGs cannot be done in 10 minutes, or at a dog show. You need a fully equipped clinic and a trained veterinary ophthalmologist with at least an hour to spare.
And: "normal" according to an ERG doesn't mean "genetic normal." The dog still could be a carrier.
In Labrador Retrievers, Chesapeake Bay Retrievers, Portuguese Water Dogs and Poodles, an ERG to rule out PRA cannot be done before 18 months of age. If a reliable ERG gives "normal" results on a dog that's 18 months or older, the dog most probably is not affected. In English Cocker Spaniels, Australian Cattle Dogs, Tollers and American Eskimo Dogs, ERG's have been less reliable.
18. Do I need an ERG on an older dog that tests as C?
If your dog is a Labrador Retriever, Chesapeake Bay Retriever or Portuguese Water Dog and is well beyond the normal age of onset for prcd-PRA (about six years), you are confident that it is showing no signs of vision loss, and you have reliable clinical exam information with no signs of vision loss, you don't need an ERG. This dog is most probably one that has a false allele. The dog could be a carrier with a false allele (but because of how markers are inherited it will never be a Pattern B; it's still a Pattern C). It could, certainly, even be normal...but it will remain a Pattern C. The situation for other breeds is different. ERG's have not been very useful due to the very late onset of the disease.
19. Does a result of "Carrier" or "Affected" mean that I can never breed my dog?
NO! OptiGen test results are meant to be used in a responsible breeding program. This does not mean that carrier or affected dogs should never be bred. It does mean that carrier and affected dogs with other desirable traits can be bred, but only to a certified, genetically “Normal/Clear" dog in order to prevent the genetic disease.
20. We were in the process of getting our dog's championship with the idea of future breeding. She has tested Affected. Do you recommend terminating this course of action?
We can't make specific recommendations about how people should handle their dogs. But health-wise and breeding-wise, there's absolutely no reason to change your plan.
She may not be affected significantly with PRA before getting her championship, and she will bear that honor for life;
And, she will never produce a PRA-affected pup if bred only to Normal dogs--but she could produce a champion.
21. If this test has a large margin of error in diagnosing carriers and affecteds, won't it limit our gene pool to the point that other problems will become more of an issue?
Whether and how we limit the gene pool is a really important issue. After all, some conditions--hip dysplasia is an example--are so genetically complex that practically every dog has the capacity for some degree of disability, be it so mild it's almost undetectable or so severe it's totally disabling. Fortunately, PRA isn't like that. Clear dogs aren't mostly clear--they're clear. The gene isn't partly recessive--it's recessive. "Carrier"s and "Affected"s bred to "Normal/Clear"s produce disease-free pups.
Indeed, the best thing about the test for prcd-PRA is that it helps keep the gene pool from shrinking. You need to pull a dog with bad hips because scientists don't know enough about the disease to prevent passing it on. But you'll never need to pull any dog because of a "Carrier" or "Affected" OptiGen prcd-PRA reading. "Carrier"s or "Affected"s bred to "Normal/Clear"s will never produce affected pups.
Often it's the breeders who suspect they have a problem that test first. If breeders test actively within the breed, they'll identify increasingly large percentages of "Normal/Clear"s--which will benefit all breeders.
22. How can I use this test to eliminate the defective gene from my line?
Find out everything you can about your dog--then breed or don't breed according to the absence or presence of traits and health considerations you have no control over. Don't let the traits you can control dictate your breeding decisions. You now have control over prcd-PRA. An OptiGen-tested "Carrier" or "Affected" dog can be bred to a "Normal/Clear" dog without producing affected offspring. "Carrier" pups can be bred again to "Normal/Clear"s. This is how you eliminate the defective gene from your line.
Your "Affected" dog's progeny will all be "Carrier"s.
23. Can an English Cocker Spaniel from outside of North America be tested for prcd-PRA?
Yes, all Cocker Spaniels can be tested for prcd-PRA.
24. How do you sum up the value of this test?
Many beautiful animals over the years developed prcd-PRA and were removed from breeding programs never to be bred again. Now these animals can be used without the fear of producing more blind dogs. The OptiGen prcd-PRA test allows breeders to present their "Carrier"s and "Affected"s with pride for all their other prize qualities.
25. Can you suggest further reading?
For detailed information for the science behind genetic testing, see Mary M. Woodsen's articles in Dog News:
"The Genetic Advantage: Baker Institute at Cornell University Releases New Tests for Progressive Retinal Atrophy," May 14, 1999.
"Marking the Spot: Genetic Testing and the Occasional False-Allele," June 25, 1999. And for a look at what many breeds are doing with veterinary genetic testing..."It's a Sure Bet: What Breeders Are Doing With the New Genetic Tests," December 3, 1999.
New York, NY 10010,
26. This is so complicated. Can't you give me "Just the Facts"?
OptiGen prcd-PRA testing in LRs, ECSs, CBRs, PWDs, Poodles, ACDs, Tollers, and Eskies: This test....identifies Pattern A = clear/normal and the result is almost 100% accurate. Identifies Pattern B = probably a carrier, but could be clear. NOT affected. Identifies Pattern C = at high risk of being either affected or a carrier, with very low chance of being clinically clear/normal. Does not definitively identify carriers or affecteds. Can be done at any age, and would be repeated only for Bs and Cs when an improved test is available.
This means…Pattern A result is not limited by the false allele. Pattern B and C uncertainties are due to the test detecting a false allele. Pattern C dogs older than the typical age of diagnosis and with clinically normal vision are most probably a carrier, or less likely, a clear/normal. Pattern A, B or C reflects a set of DNA markers. They will never change unless the test is revised. The Pattern will always remain the same and be passed on to offspring. You now can…
avoid producing affected pups by breeding Pattern B or C to Pattern A.
Eliminate prcd-PRA disease from the breed. Safely keep Pattern B or C dogs in your breeding program. Eliminate ERG’s to test for prcd-PRA disease in Pattern A and B dogs.
Please note…there is no estimate of the frequency of the false allele at this time, although it is much lower with the recently improved tests. Researchers are working hard to identify the actual gene mutation and remove the uncertainties of the B and C.
27. Do you want to learn more about OptiGen?
More information can be found on our site...just type our address... www.optigen.com in the URL line of your browser.