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Health Testing for Degenerative Myelopathy

The next important health test to require from your future breeder is for Degenerative Myelopathy. DM is a disease affecting the spinal cord, resulting in progressive weakness and paralysis, beginning in the hind end and advancing over time to the torso and front limbs. DM is similar to some of the forms of human amyotrophic lateral sclerosis (ALS, more commonly known as Lou Gehrig’s Disease). Some of the research that went into studying DM in dogs was used to understand ALS in humans.

I trust you’ve arrived here because you agree that health testing is important - but before we get into the details, I really want to drive home the fact that this disease is devastating. Ask anyone who has lived it with their own corgi. A corgi’s lifespan is blessedly longer than average - 12 years is typical, and 16 year olds are not a rarity. While you read about this condition, ask yourself, how soon would your heart break watching your beloved friend deteriorate?

It is unforgivable to steal happy and active years from a dog’s life, time that is precious beyond measure to the family that loves them, when that pain is preventable. It is abhorrent to mortgage a dog’s golden years to save less than $100 on a test. That cost is passed off to the family of the puppy, who may not have the finances to provide their beloved family member expensive physical therapy, a wheelchair, or other interventions.

The good news: this is a test that is fairly easy for the Average Joe to understand. The test for this condition was created fairly recently (2008), so there are dogs alive now that were born BEFORE this test was available. The inheritance is the type of simple inheritance you may remember from biology class (Mendel and his peas). Dogs will either have a clear result (no copies of the gene), carrier (having 1 copy), or affected/at risk (2 copies). If a dog is a carrier, they must be bred to a clear dog in order to not produce At Risk puppies.

In its early stages, the symptoms of DM resemble osteoarthritis (arthritis). There is also a loss of coordination (ataxia) in the hind limbs. They wobble when walking, knuckle over, or drag their feet. This can first occur in one hind limb and then affect the other. In these early stages, a dog will do better running than walking, and better walking than standing. One of the first deficits will be proprioception, or the ability to track where their feet are. A foot sliding out from under themselves will not be corrected, and they trip over themselves. As the disease progresses, the brain is unable to communicate with the limbs, and the dog begins to have difficulty standing.

The inability to control the limbs gets progressively worse until the dog is unable to walk. The clinical course can range from 6 months to 1 year before dogs become paraplegic. If signs progress for a longer period of time, loss of urinary and fecal continence may occur, and eventually weakness will develop in the front limbs. The disease generally runs its course over 4 years from the onset of symptoms to death. Death is caused from asphyxiation when the affected dog loses control over the ability to breathe - unless other age-related conditions cause death, or the owner chooses to humanely euthanize. Although DM is not considered to cause pain to an affected dog, it clearly impacts their quality of life.

DM is strongly suspected in dogs where they have at-risk genetics, and all other causes for neurologic disease are ruled out. Many of the symptoms of DM match the symptoms of Intervertebral Disk Disease (IVDD), and it’s possible for a dog to have both IVDD and DM. Therefore confirming this diagnosis requires a necropsy (dog autopsy, or an examination after a dog has died to determine the cause of death).

One common myth I have seen perpetuated as justification for not testing: The test for DM is not accurate. It’s true that any test can be invalid due to human error. It is also true that in affected/at risk dogs (two copies of the SOD1 gene), 98.9% of dogs will not develop the disease. You may like those odds - unless your best friend is that 1 out of 100. Saying we should not be testing is like saying we shouldn’t have life rafts on ships, because shipwrecks are incredibly rare.

Another myth is that DM does not kill dogs - if it affects them, it will be when they are very old, and they may die of something else and not actually DM. That is unfortunately not true - although on average symptoms can begin around age 8, there have been reports of DM in dogs as young as 5. Claiming that DM is not a severe illness, and won’t impact the dog negatively, is an untrue and unacceptable reason to not test every dog for DM prior to breeding.

Although it is essential to test for DM and know the status of every dog bred, that does not mean that only clear dogs should be bred. Because there are still many carriers in the breeding population, it would be disastrous to “throw out the baby with the bath water” for every dog with one copy of the gene. Dogs with one copy can safely be bred to a clear dog without risking the health of the puppies. In the case of Pembrokes, there are currently not enough dogs in the breeding population to only ever breed carriers to clears - meaning, it’s possible you will find a responsible breeder who has weighed the pros and cons of a match, and may decide to breeder two carriers together, which could result in affected puppies. It may not be the decision I would make, but you would have to speak to the breeder to understand their reasoning, and no matter what, the breeder should accept responsibility for the health of any puppy they produce.

This is a condition that can be controlled, and perhaps given time, completely eliminated from the breed. At minimum, expect your breeder to test for DM, so they can use it as one piece of the puzzle to balance the strengths and weaknesses of a breeding dog.

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