Boxers and Degenerative Myelopathy (DM / SOD1): What the Research Actually Shows

The short answer: The Boxer (AKC #17 in 2024) is one of the breeds in which the SOD1 degenerative myelopathy (DM) variant was first described (Awano et al. 2009). DM is a progressive, adult- to senior-onset degeneration of the spinal cord, often compared to ALS in people. Inheritance is autosomal recessive with age-related incomplete penetrance, so the DNA test returns a risk classification — clear (N/N), carrier (N/DM), or at risk (DM/DM) — not a diagnosis. A carrier is generally not expected to develop DM, and even an at-risk dog may never develop it. Only a veterinarian can diagnose DM clinically, by ruling out other spinal problems that look similar. A one-time DNA test is useful for breeding decisions and owner awareness. There is no cure; care is supportive.

What DM and the SOD1 gene are

SamSo the SOD1 variant is basically the switch that turns DM on, right?

Elena MarshNot quite a switch — Awano et al. (2009) showed it’s the major risk variant, but it works with age and incomplete penetrance, so having it raises risk without guaranteeing disease.

Degenerative myelopathy (DM) is a slowly progressive disease of the spinal cord that typically begins in adult or senior dogs. It gradually damages the nerve pathways that control the hind limbs, and it is frequently likened to amyotrophic lateral sclerosis (ALS) in humans because of similarities in how the nervous tissue degenerates.

The major known risk factor is a variant in the SOD1 gene, specifically the c.118G>A mutation identified by Awano and colleagues in a 2009 study published in PNAS. Dogs carrying two copies of this variant fall into the highest risk category, but the presence of the variant describes risk — it does not by itself mean a dog has, or will develop, the disease.

The Boxer and DM

SamA coworker read that “most Boxers” carry the DM gene — is that a real statistic?

Elena MarshThere’s no single global figure — Zeng et al. (2014) found allele frequencies vary by breed and population, so numbers from one group don’t apply to all Boxers.

The Boxer is a well-established American breed, ranking #17 on the American Kennel Club’s most popular breeds list for 2024. It is also historically important to DM research: the Boxer was among the breeds in which the SOD1 variant was originally described in the Awano et al. (2009) work.

It is worth noting that how common the SOD1 variant is varies considerably by breed and by geographic region and testing population. Later work, such as Zeng et al. (2014), documented that allele frequencies differ across breeds, so there is no single global number that describes every Boxer everywhere.

Why DM matters

SamIf my dog’s back legs got weak, wouldn’t a vet just know it’s DM?

Elena MarshNot immediately — DM is a diagnosis of exclusion, so a vet first rules out mimics like intervertebral disc disease, which can look similar but is often treatable.

When DM does develop, it usually starts as gradual, typically painless weakness in the hind limbs, often noticed first as scuffed nails, wobbling, or a dog that crosses its back legs. Over a period of months it can progress toward hind-limb paralysis and eventually affect the front limbs. There is no cure, and management is supportive — physical therapy, mobility aids, and attentive nursing care can help maintain quality of life.

Critically, DM is a diagnosis of exclusion. Its early signs can closely mimic other spinal conditions, especially intervertebral disc disease, which is often treatable. That is why a veterinarian must rule out those alternatives before attributing signs to DM, and historically definitive confirmation has been possible only after death through examination of the spinal cord.

Recessive inheritance and incomplete penetrance

SamSo a carrier and an at-risk dog are basically the same level of worry?

Elena MarshNo — a carrier (one copy) is generally not at risk, while at-risk means two copies; but even then, incomplete penetrance means it may never develop DM (Awano 2009).

The SOD1 DM variant is inherited in an autosomal recessive pattern with age-related incomplete penetrance. DNA tests translate a dog’s genotype into three risk classes: clear (N/N, no copies), carrier (N/DM, one copy), and at risk (DM/DM, two copies).

A carrier, with just one copy, is generally not expected to develop DM, though it can pass the variant to offspring. An at-risk dog carries two copies and sits in the highest risk group — but incomplete penetrance means that even an at-risk dog may never actually develop the disease within its lifetime. Two copies signal elevated risk, not certainty.

What the DNA test can and cannot tell

SamThen what’s the point of testing if it can’t tell me my dog will get DM?

Elena MarshIt gives a risk class per the SOD1 variant (Awano 2009) — that’s valuable for breeding choices and awareness, even though only a vet can diagnose DM clinically.

The DNA test reports a risk classification for the known SOD1 c.118G>A variant — it does not diagnose, predict with certainty, prevent, or treat DM. Only a veterinarian can diagnose the disease clinically, and only after ruling out other spinal problems. A “clear,” “carrier,” or “at risk” label describes probability and breeding implications, not a confirmed medical condition.

Where the test genuinely helps is in breeding decisions and owner awareness: knowing genotypes lets breeders plan matings to reduce the number of at-risk puppies, and it prompts owners to watch for early signs and seek a proper veterinary workup if problems appear. Because it covers this specific, well-characterized variant, a single test result reflects the dog’s genotype for life.

FAQ — Frequently Asked Questions

Q. My Boxer tested “at risk” for DM — will it definitely get DM?
No. “At risk” means the dog carries two copies of the SOD1 variant, placing it in the highest risk group, but because DM shows incomplete penetrance, an at-risk dog may never develop the disease. It is a risk classification, not a diagnosis.

Q. Is a “carrier” dog going to develop DM?
A carrier has one copy of the variant and is generally not expected to develop DM. However, a carrier can pass the variant to offspring, which matters for breeding decisions.

Q. Can DM be prevented or cured?
There is no cure and no proven way to prevent DM, and the DNA test does not prevent or treat it. Care is supportive — physical therapy, mobility aids, and nursing care to help maintain quality of life.

Q. Is the DNA result valid for life?
A dog’s genotype does not change, so the result for this known SOD1 variant reflects the dog’s status for life. It still does not replace a veterinary diagnosis if clinical signs appear.

References

• Awano T, et al. (2009) Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles ALS. PNAS 106(8):2794-2799. https://pubmed.ncbi.nlm.nih.gov/19188595/
• Zeng R, et al. (2014) Breed distribution of SOD1 alleles previously associated with canine degenerative myelopathy. J Vet Intern Med 28(2):515-521. https://pubmed.ncbi.nlm.nih.gov/24524809/
• Orthopedic Foundation for Animals (OFA) — Degenerative Myelopathy. https://ofa.org/degenerative-myelopathy/
• American Kennel Club — Most Popular Dog Breeds. https://www.akc.org/

About the author

Elena Marsh

Editor & writer (not a veterinarian)

A writer with a molecular-biology background and a lifelong dog and cat owner. Not a veterinarian — she translates peer-reviewed genetics research and primary data into plain language, always as information rather than diagnosis.