Degen. Myelopathy

According to our health survey, Degenerative Myelopathy (DM) is not a major problem in our breed, but it does occur. The University of Missouri is studying this disease and is very interested in receiving specimens and DNA from affected dogs, including Deerhounds. Liz Hansen, who is working on this project, explains:

When the mutation was first discovered in Pembroke Welsh Corgis & Boxers, then also demonstrated in Chesapeake Bay Retrievers, German Shepherd Dogs, and Rhodesian Ridgebacks, the idea that the same mutation could be present and causing disease in such unrelated breeds was unexpected—most disease-causing mutations discovered so far are breed specific, or found in a small set of related breeds. We made our initial recommendation with an abundance of caution, not wanting to overstate the possible distribution of this mutation.

Since the original discovery and with additional testing, and submission of spinal cord sections, we now have definitively proven DM caused by the mutation we discovered in 25 different breeds, and in mixed breed dogs. The breeds proven are as varied and different in their background as Pugs, Bernese Mountain Dogs, Kerry Blue Terriers, and Poodles. We have also DNA tested over 22,000 dogs representing 215 breeds and mixed breed dogs, and have found the mutation present in 110 breeds so far, plus mixed breed dogs. All of this evidence suggests that the mutation identified is widespread and very ancient in dogs, and could appear in essentially any breed.

With respect to Scottish Deerhounds, we have DNA tested 37 individuals so far. One of these was reported to have clinical signs suggestive of DM and the sample was sent by a neurologist; the remaining 36 we randomly screened from samples existing or recruited for the screening survey from dogs at dog shows (I carried sampling kits with me to shows for about a year, looking for breeds that we had few or no samples from!). All 37 of the Deerhounds we have tested have tested NORMAL for this mutation, including the clinical case. The dog with clinical signs is, to my knowledge, still alive. If the dog continues to progress as a typical DM case would, it will be very important to recruit a cord sample from that dog for evaluation. (The “gold standard” for proving DM has been a post-mortem examination of the cellular changes in the spinal cord. We used this to prove the relationship between the mutation we found, clinical signs, and the “signature” changes to the cord.)

If there are other Deerhounds showing clinical signs suggestive of DM, it would be a good idea to test these dogs as well, and we need to recruit spinal cord samples from those that look like DM. If examination of the cord does not indicate DM, it would be important to try to better understand just what disease is causing the symptoms observed in these dogs. If we see the cellular changes typical for DM in a cord from one of the symptomatic Deerhounds, but the dog tested normal or carrier for the mutation first discovered, we would re-sequence the gene to look for another mutation at work in this breed.

The mutation we discovered initially is in the SOD1 gene. Mutations in the equivalent gene in humans are responsible for the most common inherited form of ALS, or Lou Gehrig’s disease. In humans, there are over 130 known mutations in the SOD1 gene (yes, it is a VERY large gene!!), all linked to ALS. In dogs, the one mutation we discovered initially was found to be responsible for every proven DM case we knew of—until last year. We had a cord sent from a Bernese Mountain Dog that had clinical signs typical for DM, but had tested NORMAL for the known mutation. The cord showed classic DM changes, which was unexpected, based on what we’d seen in over 100 cords examined previously. With this information in hand though, we re-sequenced the SOD1 gene for this dog, and found a second mutation at work in this individual. Since then we have screened all the BMD samples we have, and found that it is present at a very low level in this breed (the original mutation is fairly common in BMD’s). We’ve also screened about 1000 dogs from other breeds, and have not seen the mutation in any other breed.

What all this boils down to is the original SOD1 mutation identified is clearly widespread and fairly common in dogs, and responsible for the vast majority of DM in dogs. The BMD example shows that there can be other mutations, but these other mutations are likely to be very rare and restricted in their distribution. We are looking at cords and searching for other possible mutations—the book is not closed on this disease by any means!

Deerhound owners with dogs showing clinical signs that look like DM should be encouraged to have the DM test run. A good diagnostic workup would be useful, although we know this can become rather expensive, depending on the diagnostics done. It is also important to let us know when one of these dogs is going to be euthanized, so that we can coordinate collection of optimal diagnostic samples with the vet or neurologist that will be euthanizing the dog. This information will help us to help the Deerhound community reduce or eliminate this problem in your breed.

For more information on this project, go to http://www.CanineGeneticDiseases.net/DM/resrchDM.htm, which has basic info, a research section, sample submission info, and more. There is a link in the research section with the protocol for spinal cord samples and contact information.

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