Degenerative Myelopathy and genetic testing
Ok, as per a request, this is being started as a new discussion. :-) The question, of course, is if this relatively new test should be part of the screening tests we expect (or at least expect to see) when we are choosing a puppy.
First, my initial post, then I'll put in a new response:
I have been puzzling over the DM test, and it makes me uncomfortable. Apparently there is a fair amount of controversy over it. So far all dogs with DM have a certain genetic marker, but it is not clear what percent of dogs with this marker develop the disease. Nor is it clear that there are not other genetic markers involved.
This is something I know a fair amount about. I have an autoimmune condition called ankylosing spondylitis, which is an inflammatory and progressive arthritis of the spine. There is a genetic marker for the disease which is present in roughly 92% of people with AS. I lack this marker. However, over 90% of people who have this genetic marker will NEVER, I repeat NEVER get AS.
Moreover, more recent long-term studies have uncovered at least 2 other genes implicated in the disease, or expression of it.
I would have zero confidence that a test for DM, which is an auto-immune disease, would at this early stage of research give any real indication of how likely an "affected" dog is of coming down with the disease. I would also have virtually no confidence that a dog that that tested clear would not come down with a disease that is symptomatically so similar to DM as to be indistinguishable in its end result. Why is that? Because I highly doubt that research in the field of autoimmune disease in dogs is so far ahead of that in humans that they can say definitively what genes cause this very sad condition.
It leaves more questions than answers. If indeed a relatively large portion of the population tests positive, but it turns out that as in humans the huge majority of "positive" animals will never, ever develop the disease, what would we do by screening them out of the gene pool?
I think the testing should be done for research, but to offer it as a breeder screening as a means of somehow insuring that a pup won't be affected is perhaps getting a little ahead of the current status of the research.
These auto-immune conditions are very complicated, are likely caused by several sets of genes causing expression or suppression of symptoms, and moreover more than likely have an environmental component that "triggers" the onset of disease activity.
Edit: This is from the very website that is conducting the research and testing for DM:
http://www.caninegeneticdiseases.net/DM/testDM.htm
"The “A” allele is very common in some breeds. In these breeds, an overly aggressive breeding program to eliminate the dogs testing A/A or A/G might be devastating to the breed as a whole because it would eliminate a large fraction of the high quality dogs that would otherwise contribute desirable qualities to the breed."
The Pembroke Welsh Corgi is one of the breeds with a very high incidence of Positive or Carrier dogs. Don't count on a flood of breeders offering up the results of their dogs tests any time soon.
Indeed, from the same site:
"Summary: We recommend that dog breeders take into consideration the DM test results as they plan their breeding programs; however, they should not over-emphasize this test result. Instead, the test result is one factor among many in a balanced breeding program. "
First, my initial post, then I'll put in a new response:
I have been puzzling over the DM test, and it makes me uncomfortable. Apparently there is a fair amount of controversy over it. So far all dogs with DM have a certain genetic marker, but it is not clear what percent of dogs with this marker develop the disease. Nor is it clear that there are not other genetic markers involved.
This is something I know a fair amount about. I have an autoimmune condition called ankylosing spondylitis, which is an inflammatory and progressive arthritis of the spine. There is a genetic marker for the disease which is present in roughly 92% of people with AS. I lack this marker. However, over 90% of people who have this genetic marker will NEVER, I repeat NEVER get AS.
Moreover, more recent long-term studies have uncovered at least 2 other genes implicated in the disease, or expression of it.
I would have zero confidence that a test for DM, which is an auto-immune disease, would at this early stage of research give any real indication of how likely an "affected" dog is of coming down with the disease. I would also have virtually no confidence that a dog that that tested clear would not come down with a disease that is symptomatically so similar to DM as to be indistinguishable in its end result. Why is that? Because I highly doubt that research in the field of autoimmune disease in dogs is so far ahead of that in humans that they can say definitively what genes cause this very sad condition.
It leaves more questions than answers. If indeed a relatively large portion of the population tests positive, but it turns out that as in humans the huge majority of "positive" animals will never, ever develop the disease, what would we do by screening them out of the gene pool?
I think the testing should be done for research, but to offer it as a breeder screening as a means of somehow insuring that a pup won't be affected is perhaps getting a little ahead of the current status of the research.
These auto-immune conditions are very complicated, are likely caused by several sets of genes causing expression or suppression of symptoms, and moreover more than likely have an environmental component that "triggers" the onset of disease activity.
Edit: This is from the very website that is conducting the research and testing for DM:
http://www.caninegeneticdiseases.net/DM/testDM.htm
"The “A” allele is very common in some breeds. In these breeds, an overly aggressive breeding program to eliminate the dogs testing A/A or A/G might be devastating to the breed as a whole because it would eliminate a large fraction of the high quality dogs that would otherwise contribute desirable qualities to the breed."
The Pembroke Welsh Corgi is one of the breeds with a very high incidence of Positive or Carrier dogs. Don't count on a flood of breeders offering up the results of their dogs tests any time soon.
Indeed, from the same site:
"Summary: We recommend that dog breeders take into consideration the DM test results as they plan their breeding programs; however, they should not over-emphasize this test result. Instead, the test result is one factor among many in a balanced breeding program. "
Replies are closed for this discussion.
Replies to This Discussion
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Permalink Reply by Beth on
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Another thought:
What if y'all aggressively breed to those "clear" dogs and find, 20 years from now, that you have inadvertently selected for another worse disease, say one that strikes healthy young dogs? Another poster mentioned that if the occurrence rate of the gene is that high, it may be inadvertently tied to something that has been carefully selected FOR over many hundreds of generations.
I found a long blog post online from a Cardigan breeder about DM testing who states that Faanconi syndrome in Basenjis was unintentionally introduced by aggressively breeding out an earlier disorder.
I'm just suggesting people take a deep breath and see what happens. -
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I will no longer respond directly to claims that we should be making demands on breeders at this point, as I have said all I want to say, often repeatedly.
I will leave the thread open and post future research as I find it. I have left the links to the OFA study site, with their breeding recommendations, for all who are interested. -
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I wanted to add an example of what I am talking about when I mention serious health issues in some breeds, for comparison:
http://www.yourpurebredpuppy.com/reviews/cavalierkingcharlesspaniel...
"The health epidemic. The biggest problem with Cavalier King Charles Spaniels today is health. This breed is in serious trouble.
Heart disease (specifically, mitral valve disease or MVD) is the number-one killer of Cavaliers. Up to HALF of all Cavaliers is likely to develop MVD by 5 years of age -- and virtually ALL Cavaliers by 10 years of age. No one should acquire a Cavalier today unless they're prepared to spend lots of money for heart monitoring and heart care.
A second serious health problem is syringomyelia, an inherited neurological disease. If a puppy is born without enough room in his skull to accommodate his brain, the back of the brain gets forced out of the skull and blocks the opening to the vertebral canal. This prevents cerebrospinal fluid from circulating freely; instead the fluid is forced into the spinal cord, causing a variety of neurological symptoms: abnormal skin sensations that cause excessive scratching around the neck or shoulder, sensitivity to touch around the neck or shoulder, yelping for no apparent reason, incoordination, and so on. (Not all symptoms are present in every dog.) Symptoms usually (but not always) appear between 6 months and 3 years old. There's no cure for this condition and current research suggests that 50% or more of the breed may be affected, though many are not yet showing symptoms."
When I talk about waiting to see out of fear of limiting the gene pool, and what problems might arise as a result, this is the sort of stuff I'm thinking of. -
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I found this very interesting. The advice is for breeders of Chesapeake Bay Retrievers, a breed with a high number of "at risk" or "carrier" dogs in the gene pool. However, to date Chessies have about 42% "clear" dogs, much higher than Corgis.
I hope the link works.
http://www.cbrs4me.com/chesapeake/Understanding-and-Applying-Geneti...
"DM has always been known to be polygenic, also known as a complexly-inherited disease. More than one gene pair controls its inheritance. No one believes that DM is a simple recessivedisease. The DM test is for a recessive mutation that controls part of the inheritance of thedisease"
"For the DM test dogs coming back "At-Risk" is the probability that the dog will laterdevelop the disease known? Are there any statistics on frequency or number seen ofaffected dogs in the general Chesapeake population?
As we do not know the other factors that cause the clinical onset of DM, we cannot predict whatpercentage of dogs testing “At-Risk” (homozygous for the susceptibility gene) will develop thedisease. Dr. Coates’ research of the Veterinary Medical Database (VMDB) showed that 13 of1,567 (0.83%) Chesapeake Bay Retrievers presenting to veterinary teaching hospitals hadclinical DM. Presently, 15% of Chesapeake Bay Retrievers test “At-Risk” for DM. It is obvious that the vast majority of “At-Risk” dogs will not develop DM."
"Is the result of this test for one gene for DM enough to advise breeders to only breed onlyCarrier and At-Risk dogs to only normals?
No. While this recommendation guarantees that no DM affected dogs will be produced, it also requires that all matings be conducted with at least one member of a class of 42% of your genepool. This significantly skews the gene pool in their direction, and reduces the influence of almost 60% of the breed’s gene pool. For a disease that affects less than one in one-hundred Chesapeake Bay Retrievers, this severe a restriction on breeding will significantly limit thebreed’s genetic diversity." -
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Permalink Reply by Kathleen Mallery on
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>"DM has always been known to be polygenic, also known as a complexly-inherited disease. More than one gene pair >controls its inheritance. No one believes that DM is a simple recessive disease
Before I tackle the above quote, let me introduce myself. I am Kathleen Mallery of Castell Welsh Corgis. We have been breeding and exhibiting Pembrokes for over 25 years. We have produced and breeder/owner/handled 4 consecutive dogs in 3 consecutive generations to top honors. We have "boo coo" dogs in performance arenas and even more with the exceptional job of being companions. I started with tested stock and have continued to test routinely over the years.
I entered this breed in the early '80's from Labradors when genetic testing was only done by a handful of corgi breeders. Then I could find about 5 that did hips and eyes. A dear friend and I came out very public about the necessity of testing in 1984 through the then Corgi Quarterly -Spring issue I believe (now Welsh Corgi Annual). We were bashed and mashed but the COE were shortly changed to include these tests.
Since then I have been instrumental in the vWD DNA test and my dogs were one of the familial groups used by the University of Missouri. Dr. Coates and I have shared more than one cup of coffee (sometimes ice cream cones!) discussing the DM issue, research progress and the direction it is going.
Now to address the above comment.
I have known GSD breeders throughout the NW for years so I have been aware of DM for a very long time. Never. and I repeat, NEVER have I heard this polygenic theory. Autoimmune, I've heard but not polygenic. I'd be interested in research data to support this theory. I don't believe Dr. Clemmons research has ever suggested this theory, although I'm sure it would be irresponsible NOT to consider it as well as other theories. We MUST consider ALL angles.
On this thread in general....I've been reading the posts some. Quite frankly, why would ANYONE NOT want to test their stock? Without the numbers we need, we will never know how penetrated this gene is! We only have 600 dogs. We need AT LEAST 1000. Are breeders afraid to know? Knowing is half the battle. What you individually decide to do with the information is your own personal decision.
Myself, I've lived with more than one of these dogs. I've helped others through it. Like the lab puppy I put down at 5 months of age because his hips were so bad he couldn't get up from a sitting pisition, Idon't want to produce another like it if I can help it. I have always line bred therefore I CAN find a common denominator in my DM dogs....it goes to a "popular sire" of a specific "line" and generation. I can't afford to lose the qualities this line gives me but I CAN afford to dilute it a little just so I can introduce something else....like the clear gene for DM. The dog I have used is a high quality dog, who eventually does go back to related ancestors. What people don't understand is the potency of a dogs impact in a pedigree depends on his potency AND how often he shows up in the pedigree...not just the first 3 generations. The way my dogs resemble the BLANDS dogs is a good example. That is the line I love the most and try to keep doubling on. Peggy Gamble, herself, agreed that I had "her look".
Adding DM as another genetic item to consider would be a lot easier if more people simply tested. If they choose not to breed forward from the test, so be it. But their results might be clear and give the rest other options. Right now, on the OFA site we really only have about 5 choices. That could be 50 or 500 choices if others would simply test. The results go into the database to help us understand the penetrance and they can do what they want with their test results.
People need to quit thinking about themselves, their reputations and their winning records and think more about preserving the breed. Unfortunate for the breed, we all do this for different reasons and, though they may argue the point, not everyone truly breeds for the welfare of the breed. If they DID, we wouldn't have the "popular sire syndrome" like we do.
I have more thoughts but this is enough for tonight. -
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I am sorry you never heard the polygenic theory. Generally speaking, with what I have learned from suffering from a genetic disease myself, I have learned that many of the more complex genetic diseases are believed to have several genes and outside factors which control expression or suppression of symptoms.
This is from the link I posted, and the person who said they all believe it to be polygenic:
"....Dr. Jerold Bell for answers. Dr. Bell is a practicing veterinarian as
well as Clinical Associate Professor of Genetics at Tufts Cummings School of Veterinary
Medicine in MA. Dr. Bell received his BS from Michigan State and his DMV from Cornell
University, NY State College of Veterinary Medicine in 1982. His areas of interest are Genetic
Disorders, Epidemiology of Defective Genes in Purebred Populations, and Breed
Improvement/Breeder Education."
Seems to me like he's a pretty good source.
In the Coates podcast I listened to, she also said they are currently looking for other genes involved, since the low incidence rate among "At Risk" dogs makes them believe there is much more at work. -
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Kathleen, I do appreciate what you are trying to do and your frustration. The current guidelines for Chessies, at least, (according to the geneticists who know a fair amount about breeding) are that for those who have DM in their lines, they should breed carriers and At Risk dogs to clears, since they are already displaying the traits.
Those who don't have DM in their line are advised to not follow that recommendation, as it would cause too much of a narrowing of the gene pool for genetic health. Again, this is Chessies with over 40% clear and it appears early on that PWC's don't have that luxury.
It must be frustrating to not find many clears when people are either not testing or not sharing the results. However, as I said, the test is barely a year old and people are still uncertain and alarmed by the numbers coming in. As more research is done and more lectures are given about breeding guidelines, that will probably start to change very gradually (or maybe suddenly, depending on what the research shows).
I am posting the best research I can find. I am not a breeder but I have enough background to understand a fair amount of what I am reading. I did not find an online transcript of a lecture to Pem owners like I found for Chessies, which is why I posted the Chessie one.
Puppy-buyers can ask for any background or testing they like. For now I will follow the guidelines laid out by the PWCCA.
Thank you for your input. I am closing the thread. -
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