The Degenerative Myelopathy Test: What a Positive Result Actually Means

The degenerative myelopathy test is a DNA test for a variant in the SOD1 gene. It is cheap, it can be run from a cheek swab, and it is one of the most widely misread results in canine genetics.

Here is the short version, because it is the part that matters. A positive result does not mean your dog has degenerative myelopathy, and it does not mean your dog will get it. The disease is inherited with incomplete penetrance, which means a dog can carry two copies of the variant and never develop signs. What you are buying is a risk figure.

That makes the test genuinely valuable for one purpose and close to useless for another. Which is which decides whether it is worth your money.

What the Three Results Mean

The disease is inherited in an autosomal recessive pattern with incomplete penetrance, which produces three possible outcomes.

Laboratories choose the wording in that bottom row deliberately. UC Davis says a dog with two copies "may have degenerative myelopathy" and states plainly that not all DM/DM dogs will develop the disease.

The University of Missouri, where the variant was identified, puts it the same way: not all dogs that have the mutation will develop the disease, so the mutation test is currently a test for risk.

Nobody publishes a reliable percentage for how many at-risk dogs go on to develop signs. Other genetic and environmental factors are involved and have not been identified, which is what "incomplete penetrance" is describing.

The Question People Actually Come With

"My dog is nine and knuckling. Will the test tell me if it's degenerative myelopathy?"

Not on its own, no, and this is the single most useful thing on this page.

A positive result in a symptomatic dog is consistent with the diagnosis. It does not confirm it, because a substantial number of healthy dogs of the affected breeds carry two copies and never develop anything. Your dog can be DM/DM and have a slow disc protrusion, lumbosacral disease, or a spinal tumour causing the signs you are watching.

A negative result is more informative, and in the useful direction: a clear or carrier result makes degenerative myelopathy very unlikely and sends the workup somewhere else.

So the test earns its place in a diagnostic workup as one input among several, alongside imaging to rule out the compressive causes. It does not replace that imaging, and a vet who offers the DNA test instead of investigating is skipping the part that could find something treatable. Our guide to degenerative myelopathy in dogs covers how the diagnosis is actually reached, including why an MRI cannot show this disease and is ordered anyway.

Where the Test Is Genuinely Worth It

Breeding. This is what the test was built for and where it works. Two clear dogs cannot produce an at-risk puppy. A carrier bred to a clear dog produces carriers and clear dogs but no at-risk ones, which is how the variant gets managed down without narrowing a gene pool by excluding every carrier from breeding.

In breeds where the variant is common, excluding all carriers would shrink the breeding population sharply and trade one health problem for the problems that come with inbreeding. Testing lets breeders pair around it instead.

Buying a puppy from an at-risk breed. Ask for the parents' results rather than the puppy's. Two clear parents settle the question entirely.

Ruling it out in an older dog with hind end signs. Worth it for the negative, as above.

Where It Is Not Worth Much

Testing a healthy adult dog for peace of mind. A clear result is reassuring. An at-risk result tells you your dog may develop a disease it may equally never develop, at an unknown probability, with nothing you can do differently in the meantime. There is no preventive treatment, no monitoring protocol that changes the outcome, and no evidence that any drug, supplement or diet alters the course of the disease.

Some owners want to know anyway, which is a legitimate reason. Just go in knowing the result does not come with an action.

Settling an argument about a dog already diagnosed. If the workup has ruled out the compressive causes and the clinical picture fits, the test adds confidence rather than certainty, and a definitive diagnosis is only possible on examination of the spinal cord after death.

Where to Get It, and What to Expect

The test is run by the University of Missouri, where the variant was found, and by university and commercial genetics laboratories including UC Davis. It is also bundled into the broad consumer DNA panels, which is how most owners end up with a result they were not looking for.

Samples are usually a cheek swab or a blood draw. Results take days to a few weeks depending on the laboratory.

One caution about the panel tests. A breed-wide panel returns dozens of results at once, and an at-risk degenerative myelopathy line in that list carries the same visual weight as a coat colour marker. Read it in the context above rather than as a diagnosis delivered by email.

If the Result Comes Back At Risk

Nothing changes today. There is no preventive step and no treatment to start.

What is worth doing is knowing the early signs, because if this dog is one of the ones that develops it, the first changes are subtle and most owners date the onset months late. Asymmetry is the thing to watch: one back leg going before the other, the hind nails on one side wearing flat, the dog clipping its own back feet on turns.

And if signs do appear, the useful move is a proper workup rather than an assumption. A positive test in the file makes it tempting to accept the obvious answer, and several of the alternatives are treatable. Our guide to an older dog whose back legs are collapsing covers what else it can be.

Equipment is a long way down the list and not something to buy in advance of need. A cart bought on the strength of a DNA result will sit in a hallway for years, possibly forever.

What is worth doing early, if the disease does arrive, is introducing a rear support dog wheelchair before it is the only option left, while the dog still has the front end strength to learn it comfortably.

Fit needs revisiting more often here than in a stable condition, because the hindquarters lose muscle steadily and a frame set six months ago will not sit right today.

The Whisker Bark adjustable dog wheelchair adjusts in height, length and width for that reason.