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INSIDE
----DIRECTOR'S COMMENTS----
The testing of DNA for a specific genetic disease is becoming more and more common place. It would be very nice if a DNA test were available for each heritable disease in purebred dogs. Each puppy could have a genetic test or battery of genetic tests and we could make much more appropriate breeding decisions. CERF serves as the repository for this information and will register dogs that have been shown by a DNA test to be free of the abnormal genetic trait.
DNA testing is a bit of a mine field at this time because there are no standards readily available to help the general public make a judgment as to the merits of one DNA test over another. When well known, credentialed scientists are involved with a specific test, one can be assured that test is accurate. But, when someone not well known or credentialed offers a DNA test, how can one know if the test will work? This is a question I have thought about a lot. Since CERF serves as the registry for some of these tests how do we know what that registration is based upon?
I asked the American Veterinary Medical Association to consider establishing a group of scientists who could judge the merits of a genetic test. This would provide information to veterinarians, breed clubs, and disease registries as to the strengths and weaknesses of the various tests that might be available. After considering this possibility they decided not to do this. This would have been a valuable service to animal owners but, it would have been fraught with some difficulty.
The CERF policy is as follows: the breed club must select the test they think will provide them with the best information for their breed. We will provide logistical support to facilitate the running of the test and register those that are found to be free of the gene defect. Some of the tests will render more information than just positive or negative. So the breed club must decide how to deal with that information. To date this has worked quite well. If your breed club wishes to pursue gene testing and a test is available, CERF stands ready to help see that this is done with the least consternation on the part of the club members.
ACVO Genetics Committee/CERF Liaison
Progressive retinal atrophy (PRA) is the name for a group of devastating eye diseases that can lead to complete blindness in dogs. PRA has been identified in numerous breeds and can occur in mixed breed dogs as well. Recently there has been much research into these inherited eye diseases to better characterize them in terms of pattern of inheritance, age of onset, and location of the causal gene mutation in the different breeds that are affected. Researchers at the Jams A. Baker Institute have identified six separately- inherited forms of PRA in dogs (see NOTE bellow). In one of these, rod cone dysplasia 1 (rcd1) of Irish setters, the gene mutation has been identified.
There are ongoing investigations attempting to identify the gene mutation in other types of PRA. Progressive rod-cone degeneration (prcd) is the most widespread form of PRA and affects many breeds including poodles, American and English cocker spaniels, Labrador retrievers and Portuguese water dogs. Many more breeds of dogs are probably also affected by prcd but this has yet to be confirmed. This form of PRA is particularly devastating because it is a late-onset disease. This means that the rods and cones (the visual cells in the retina) develop normally and then later (at about 1 year of life) degenerate. Prcd starts with night blindness and progresses to total blindness at 3 to 5 years of age. The late onset of clinical signs in prcd is particularly devastating to breeding programs because many dogs have already been bred prior to the onset of symptoms. Thus the development of a genetic test for this disease which could determine both affected and carrier animals would be particularly useful.
The researchers at the James A. Baker Institute have developed a marker-based test for prcd and it will soon be commercially available for Portuguese water dogs, Chesapeake Bay retrievers, English cocker spaniels and Labrador retrievers (see NOTE bellow). This test is based on the fact that the researchers have found a set of genetic markers on the canine chromosome 9 that usually indicate the presence of the gene mutation that causes prcd (see NOTE bellow). These markers are groups of alleles (genes occupying corresponding sites on pairs of chromosomes) which do not cause the disease but show up in individuals that have or carry the disease (see NOTE bellow). The identification of these markers close to the gene mutation of prcd, form a genetic "fingerprint" for the disease (see NOTE bellow). Although the gene mutation that causes prcd has not been found, every dog that is affected with prcd has 2 copies of the genetic marker and every dog that does not have the marker is clear of prcd (see NOTE bellow).
Unfortunately, this test for the genetic marker is not as accurate in diagnosing prcd as it would be if the actual gene mutation was found. This is because dogs that are not affected by prcd may have the marker alleles present and thus there may be false positives obtained with this test. This does not decrease the value of having dogs tested for the marker genes however. Animals without the gene marker are either completely clear of the disease (are neither carriers nor affected dogs) and may be safely used for breeding. Dogs that are positive for the gene marker may be either false positives or may be carriers of the disease or may be affected by it. If an animal tests positive for the gene marker, it may either be removed from the breeding population or test bred with a known affected dog in order to determine whether he or she is a false positive. The marker test may be done at a very early age, so potential breeding animals may be selected when they are still puppies.
Research is ongoing to improve the test for use in other breeds, particularly poodles, and to determine the form of PRA that affects other breeds. Thus, genetic testing may be available for other breeds in the future.
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NOTE:
Breakthroughs in Sight: Progress in PRA Research. James A. Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University.
The following are some commonly asked questions that we've received:
Q: Have the fees for CERF Certification changed?
A. Fees have increased by $2.50 for both Re-CERFS and initial
registrations. We will honor the fees indicated on the back of the form,
if you should still get an older form. Remember to still make one check out
for all exams payable to CERF in U.S. funds.
Q. What is the newest book available?
A. Finally, a new 1999 edition of the Ocular Disorders Presumed to be
Inherited in Purebred Dogs book is due out in July. The cost will remain the
same; however, you will notice a big change in the format.
OptiGen, our DNA testing site has expanded. In conjunction with this CERF
is expanding their DNA Registry. In Irish Setters there has been a DNA test for
PRA, which has been registered through CERF since 1994. Now available is a test
for CLAD (Canine Leukocyte Adhesion Deficiency). This is an inherited, fatal
immunodeficiency disease in which pups that inherit two recessive genes usually
die early from multiple infections.
OptiGen is also doing PRA testing on Portuguese Water Dogs, Chesapeake Bay Retrievers, and English Cocker Spaniels. Coming in September there will be a PRA test for Labrador Retrievers also. Another test available is for CSNB (Congenital Stationary Night Blindness) for Briards.
The fees for the tests on Irish Setters are $150 each ($135 - test; $15 - CERF Registration). If you should choose to do both tests simultaneously the fees would be $225 ($200 - both tests; $25 - both CERF Registrations). The Briard CSNB test is available for $175 ($160 - test; $15 - CERF Registration). All payments and orders will be made through OptiGen. Order forms can be retrieved via the Internet at www.optigen.com or genetest@optigen.com or by phone at (607) 257-0301.
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