DM testing in dogs is a DNA test that checks for a specific gene mutation linked to degenerative myelopathy, a progressive spinal cord disease that gradually destroys a dog’s ability to use its hind legs. The test identifies whether a dog carries zero, one, or two copies of a mutation in the SOD1 gene, which plays a role in protecting nerve cells from damage. It’s used both by breeders making mating decisions and by veterinarians trying to figure out why an older dog is losing coordination in its back end.
What Degenerative Myelopathy Does
Degenerative myelopathy is a slow, painless breakdown of the nerve fibers in the spinal cord. It typically appears in dogs around eight years of age or older, and the first signs usually show up in one hind leg before spreading to both. Early symptoms include difficulty rising, hind limb weakness, loss of coordination, muscle wasting, and scuffed or worn toenails on the back feet from dragging them during walks.
The disease occurs most commonly in German Shepherds, Corgis, and Boxers, but it also affects Rhodesian Ridgebacks, Chesapeake Bay Retrievers, Poodles, Labrador Retrievers, Siberian Huskies, Collies, and Kerry Blue Terriers, among others. There is no cure, and the condition progresses over months to years until the dog can no longer walk.
How the Gene Test Works
The test looks for a specific mutation in the SOD1 gene: a single-letter change in the DNA code that swaps one amino acid for another in the protein the gene produces. SOD1 normally helps protect cells from oxidative damage. When both copies of the gene carry this mutation, the protective mechanism breaks down, and nerve fibers in the spinal cord gradually deteriorate.
Every dog inherits two copies of the gene, one from each parent, so the test returns one of three results:
- Normal/Clear (N/N): Two normal copies. The dog will not develop DM from this mutation and cannot pass it to offspring.
- Carrier (N/A): One normal copy and one mutated copy. The dog is extremely unlikely to develop DM itself but can pass the mutation to roughly half its puppies.
- At-Risk (A/A): Two mutated copies. The dog has a significantly elevated risk of developing degenerative myelopathy, though not all at-risk dogs will show symptoms.
That last point is important. The mutation has what geneticists call “incomplete penetrance,” meaning some dogs with two copies live out their lives without ever developing clinical signs. The test identifies risk, not a guarantee. A dog that tests A/A may never show symptoms, while a dog that does show symptoms still needs other conditions ruled out before DM can be presumed.
Collecting the Sample
The test uses cheek cells, not blood. You collect the sample at home using small brushes provided by the testing laboratory. The process is straightforward but has a few rules that matter for accuracy.
Your dog should not eat or drink for at least one hour before collection. You place the brush between the gums and the inside of the cheek, press lightly on the outside of the cheek, and rub or rotate the brush back and forth for about 15 seconds. Then you wave it in the air for 20 seconds to dry it before sliding it back into its sleeve. Most labs send three brushes per dog, and each one should be used on a different spot along the gums and cheeks.
A few common mistakes can ruin a sample. You want cheek cells, not saliva, so avoid collecting drool. Don’t rub the brush on the tongue or teeth. If you’re testing puppies, isolate each one from the mother and littermates for an hour beforehand, since a puppy that recently nursed can have the mother’s DNA in its mouth, contaminating the result. If you’re swabbing multiple dogs, wash your hands between each one.
What the Test Cannot Tell You
A positive genetic result (A/A) does not, on its own, diagnose degenerative myelopathy. The SOD1 test identifies dogs that are genetically at risk, but several other spinal cord conditions, including disc disease and spinal tumors, can look identical in a living dog. A veterinary neurologist diagnoses DM by ruling out those other causes through imaging and neurological exams. Even then, the diagnosis during a dog’s lifetime is considered presumptive. The only definitive confirmation comes from examining spinal cord tissue after death.
This distinction matters practically. If your older dog is dragging its hind feet and tests A/A for SOD1, DM becomes the leading suspect, but your vet will still want to check for treatable conditions like a herniated disc that could cause the same symptoms. The genetic test is one piece of the puzzle, not the whole picture.
Why Breeders Use It
DM testing is a standard part of responsible breeding programs for at-risk breeds. The mutation is common enough in some populations that simply excluding every carrier from breeding would shrink the gene pool dangerously. In German Shepherds from Uruguay and Paraguay, for example, roughly 26% of dogs tested were carriers and about 8% were at-risk (homozygous for the mutation). The overall frequency of the risk allele in that study population was 21%.
The general breeding guideline is to avoid mating two carriers together, since that pairing has a 25% chance of producing at-risk puppies. A carrier bred to a clear dog will never produce at-risk offspring, though about half the litter will be carriers themselves. This approach lets breeders gradually reduce the mutation’s frequency without eliminating otherwise excellent dogs from breeding programs.
Cost and Where to Get It
The Orthopedic Foundation for Animals (OFA) registers DM test results and charges $15 per test for result filing. The genetic test itself is available through several laboratories, including the UC Davis Veterinary Genetics Laboratory, and typically costs between $45 and $75 depending on the lab and whether you’re bundling it with other genetic screens. Many breed-specific health panels already include DM testing alongside checks for other inherited conditions.
Results generally come back within two to four weeks. If you’re buying a puppy from a breed prone to DM, asking the breeder for the parents’ DM test results is reasonable and increasingly expected. For dogs already showing neurological symptoms, your veterinarian can order the test as part of the diagnostic workup.