Dog DNA Tests: What a Health Result Can and Can't Tell You
More than half of dogs carry at least one disease variant. What carrier and at-risk results mean, why at-risk isn't a diagnosis, and when a test helps.
Written by thecanineledger
A study of more than a million dogs tested by a commercial DNA company found that “57% of dogs carry at least one copy of a studied Mendelian disease-associated variant” (Donner et al., PLOS Genetics 2023). A Mendelian disease is one caused mainly by a single gene.
While that sounds alarming, carrying a variant is not the same as having, or getting, the disease. This page explains what a health DNA result means, why “at risk” is not a diagnosis, and when a test is genuinely useful.
1. What a health DNA test looks for
Known single-gene variants. Commercial panels check your dog’s DNA for variants already linked to specific diseases. The 2023 study screened for 250 of them.
It’s a large and growing market. The study’s authors note that “commercial screening is being offered for most of them worldwide.” A 2018 comment in Nature by three US researchers warned that “It is too easy for companies to sell false hope” (Moses et al., Nature 2018, opening paragraph only).
Who did the big study. The authors of the 2023 study work for a commercial dog DNA testing company, and the dogs had been tested by it, either bought direct by owners or through vet clinics.
Our note: The Nature comment is paywalled. We read only its standfirst and opening paragraph.
2. Carrier, at risk, or clear
For most variants, a dog gets one copy of each gene from each parent.
| Result | What it usually means |
|---|---|
| Clear | No copies of the variant found |
| Carrier | One copy of a variant that needs two copies to cause disease. The dog is unlikely to be affected by that variant, but can pass it on |
| At risk | Two copies of a variant that needs two, or one copy of a variant that needs only one |
The 2023 study defines “genetically at risk” the same way: “dogs with two copies of a presumed recessive disorder or dogs with one copy of a presumed dominant disorder”.
Our note: The table simplifies how inheritance works, and test companies use slightly different labels.
3. “At risk” is not a diagnosis
Not every at-risk dog gets sick. In degenerative myelopathy, a spinal cord disease of older dogs, a 2014 study followed dogs with two copies of the main variant. It found that “18 of the 30 dogs with the homozygous SOD1:c.118A genotype developed clinical signs consistent with DM” (Zeng et al., Journal of Veterinary Internal Medicine 2014). Homozygous means two copies. The other 12 didn’t, at least by the time of the study.
Many variants are poorly understood. The 2023 study says there is “uncertainty regarding their functional and clinical impact in ancestry backgrounds beyond the discovery breed.” A variant found in one breed may behave differently in another, or in a mixed breed.
Only some are proven. Using vet records, the study found “evidence of full penetrance for 10 variants, and plausible evidence for clinical significance of 22 variants”. Full penetrance means every at-risk dog it checked showed the disease.
What to do with an at-risk result. Take it to your vet. Don’t change treatment, or make an end-of-life decision, on a DNA result alone.
4. What a clear result can’t tell you
The panels focus on single-gene variants. Many common problems in dogs, such as arthritis and most cancers, aren’t caused by one known variant, so a panel can’t rule them out.
Some known variants explain only part of the risk. For copper liver disease in Labradors, gene variants found so far “accounted for only 12% of total heritability”.
→ Chronic Hepatitis and Copper in Dog Food
Our note: “Many common problems … aren’t caused by one known variant” is our own summary.
5. When a test genuinely helps
Breeding. This is where single-gene tests are most useful. For degenerative myelopathy, the 2014 study concluded that “breeding to avoid the production of SOD1:c.118A homozygotes is a rational strategy.”
Not over-excluding dogs. The 2023 study says good data also help “ensure that dogs carrying a non-causal variant are not unnecessarily excluded from breeding programs.” A carrier can often still be bred, to a clear dog.
Your vet’s planning. Some results may matter for future care. The 2023 study found that factor VII deficiency, a clotting variant, “presents as subclinical bleeding propensity”. Your vet may want to know before surgery.
Buying a puppy. Ask the breeder which tests the parents have had, and the results. Test results for the parents of a pedigree puppy can be more useful than testing the puppy afterwards.
Our note: The last two paragraphs are our advice.
→ Choosing a Breed or a Mix: The Health Data Breeders Don’t Lead With · → Breed and Lifespan: What the UK Primary-Care Data Shows
6. What we could not verify
| Commonly said | What we found |
|---|---|
| “At risk means my dog will get the disease” | No. In one study, 18 of 30 at-risk dogs developed degenerative myelopathy. |
| “A clear result means a healthy dog” | No. Panels only check known single-gene variants. |
| “Carriers shouldn’t be bred” | Not necessarily. Carriers can often be bred to clear dogs. Ask your vet or breed club. |
| “Every variant on the report is proven” | No. The impact of many variants beyond the breed they were found in is uncertain. |
| “Mixed breeds don’t need testing” | Not so simple. The large study’s authors argue recessive testing is useful in mixed breeds too. They sell the tests. |
Sources
- Donner J, Freyer J, Davison S, et al. Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLoS Genet 2023: 1,054,293 dogs. Authors employed by a commercial dog DNA testing company
- Zeng R, Coates JR, Johnson GC, et al. Breed distribution of SOD1 alleles previously associated with canine degenerative myelopathy. J Vet Intern Med 2014: genotype and pathology study
- Moses L, Niemi S, Karlsson E. Pet genomics medicine runs wild. Nature 2018. ⚠️ not peer-reviewed. Comment; only the opening paragraph read (paywalled)
- Strickland JM, et al. Hepatic copper concentrations in 546 dogs (1982–2015). J Vet Intern Med 2018: retrospective study
Always confirm with your vet before acting on anything on this page.