IVDD Genetic Testing: CDDY, FGF4 & What the Results Mean
CDDY and FGF4 genetic testing can tell you if your dog carries the IVDD risk gene — but a positive result isn't a diagnosis. Here's how to read the results and…
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An IVDD genetic test can tell you whether your dog carries the mutation that drives early disc disease — and that information, used wisely, can genuinely change how you care for them.
What Exactly Are CDDY and CDPA — and Why Do Both Matter?
CDDY and CDPA are two separate genetic traits that affect a dog’s body structure, and they’re often confused with each other. CDDY (chondrodystrophy) is the one directly tied to IVDD risk. CDPA (chondrodysplasia) affects limb shape but is not associated with the same disc disease risk.
Here’s how they break down:
CDDY (Chondrodystrophy): Caused by the FGF4-12 retrogene on chromosome 12. This mutation causes premature calcification of the intervertebral discs — meaning the discs lose their shock-absorbing properties far earlier than they should. This is the direct precursor to Hansen Type I IVDD, the kind that can go from “a little stiff” to “completely paralyzed” within hours. CDDY is also responsible for the classic low-slung, long-backed body shape in breeds like the Dachshund.
CDPA (Chondrodysplasia): Caused by the FGF4-18 retrogene on chromosome 18. This mutation produces short, bowed limbs but does not carry the same disc calcification risk that CDDY does. A dog can have CDPA without having CDDY — and that matters when you’re interpreting results.
Why the distinction is important: A dog that tests positive for CDPA only (no CDDY) has the short-limb body shape but lower disc disease risk. A dog positive for CDDY — with one or two copies — has the elevated IVDD risk regardless of body shape. Many breeds carry both mutations simultaneously, which is why interpreting a panel result requires understanding what each gene actually does.
- CDDY: Chondrodystrophy — the disc-disease risk gene (FGF4-12 retrogene)
- CDPA: Chondrodysplasia — the short-limb shape gene (FGF4-18 retrogene), not directly linked to IVDD risk
- Hansen Type I IVDD: The acute, explosive disc herniation type associated with CDDY-positive dogs
- Retrogene: A copy of a gene that has been reinserted into a different location in the genome — this is what FGF4-12 and FGF4-18 are
Which Breeds Should Get Tested?
Breeds commonly affected by chondrodystrophy — and therefore the ones most relevant for IVDD genetic testing — include Dachshunds, Corgis, Basset Hounds, French Bulldogs, Shih Tzus, Pekingese, Beagles, and Cocker Spaniels. You can find a broader breakdown in the complete at-risk breed list.
Testing makes particular sense in three situations:
Breeders selecting breeding pairs: Two CDDY/CDDY (homozygous) parents will produce puppies that all carry two copies of the risk gene. Breeders who test can make intentional choices to reduce the frequency of homozygous puppies over generations.
Buyers evaluating a puppy or adult dog: If you’re considering a Dachshund or French Bulldog puppy and the breeder can provide genetic test results, that information helps you understand what level of monitoring and precaution makes sense from day one.
Owners who want clearer individual risk information: Even if your dog is already living with you and already a high-risk breed, knowing whether they carry one copy versus two copies of the CDDY gene can help you and your vet have more informed conversations about prevention and monitoring.
How Do You Read IVDD Genetic Test Results?
Results for the CDDY mutation come back in one of three forms, and each means something different.
| Result | What It Means | IVDD Risk |
|---|---|---|
| N/N (Clear) | No copies of the FGF4-12 retrogene | Lower risk — disc disease still possible but less likely and typically later onset |
| N/CDDY (Carrier / One copy) | One copy of the mutation (heterozygous) | Elevated risk; chondrodystrophic disc changes likely |
| CDDY/CDDY (Affected / Two copies) | Two copies of the mutation (homozygous) | Highest risk; disc calcification expected early in life |
disableddogcare.comA few things worth knowing about these numbers: “N/N clear” doesn’t mean invincible. Hansen Type II disc disease — the slower-onset degenerative type seen in larger breeds — can occur in dogs without the CDDY mutation. And “CDDY/CDDY” doesn’t mean your dog is guaranteed to herniate a disc. It means they are very likely to have calcified discs, and those calcified discs are at higher risk of rupturing under the right circumstances.
The UC Davis Veterinary Genetics Laboratory is one of the most widely used academic labs for this test and offers clear result interpretation alongside their panels. Many veterinarians submit samples on your behalf, or you can order a kit directly.
- It cannot predict when or whether a disc will herniate
- It cannot identify which specific disc is already calcified
- It does not replace neurological exams or imaging
- A clear result does not mean your dog is immune to disc disease
Does a Positive Result Change How You Should Care for Your Dog?
Yes — but the changes are practical, not panicked. A CDDY-positive result is not a sentence. It’s a prompt to be proactive.
For owners, a positive result generally supports:
Weight management: Excess body weight increases the mechanical load on already-vulnerable discs. Keeping a CDDY-positive dog lean is one of the highest-impact things you can do. This is consistent with broad veterinary consensus on disc disease prevention.
Activity modifications: Repetitive high-impact movements — jumping on and off furniture, running up stairs dozens of times a day — put extra stress on calcified discs. You don’t have to wrap your dog in bubble wrap, but using ramps instead of furniture jumping and managing rough play is genuinely worthwhile.
Pet insurance timing: A CDDY-positive result is useful information for insurance decisions. IVDD surgery can run into thousands of dollars. If your dog hasn’t had a disc episode yet, getting coverage before any incident becomes a pre-existing condition matters. There’s a full discussion of this in the pet insurance and IVDD article.
Knowing the early warning signs: Owners of CDDY-positive dogs benefit from being fluent in what early IVDD looks like. Hunched posture, reluctance to jump, yelping when touched, and subtle changes in gait are all worth taking seriously in a dog you know is genetically at-risk. The IVDD symptoms overview is a good reference to bookmark.
- Discuss the result with your vet and ask about baseline imaging if it’s appropriate for your dog’s breed and age
- Start or continue weight management — this is one of the most evidence-supported prevention strategies
- Set up ramps for furniture and car access if you haven’t already
- Review pet insurance options before any incident occurs
- Learn the early warning signs of IVDD so you catch an episode early
What Are the Real Limits of Genetic Testing?
Genetic testing for IVDD risk is genuinely useful — but it has limits that are worth being honest about.
It tells you about one mechanism, not all of them. The CDDY test is specific to the FGF4-12 mutation. There are other genetic and environmental factors that contribute to disc disease, and not all of them are captured by current tests.
It doesn’t tell you which disc is at risk. Even a dog that is CDDY/CDDY homozygous may have some discs that are more calcified than others. The only way to see that is with imaging — typically an MRI or CT scan. If your vet is considering baseline imaging for a high-risk dog, the IVDD imaging article walks through what each type shows.
Homozygous results are common in some breeds. Dachshunds, for instance, have such a high prevalence of the CDDY mutation that most of the breed tests positive. A result that sounds alarming may simply reflect breed-level baseline reality — which is why context matters.
Testing informs breeding decisions, but doesn’t eliminate risk overnight. For breeders, selecting against homozygous pairings reduces the proportion of high-risk puppies over generations. But it’s a long-term effort, not a one-generation fix, and involves balancing other important health and temperament traits simultaneously.
The research identifying these specific retrogenes as the cause of chondrodystrophy in dogs was largely advanced through work at the UC Davis School of Veterinary Medicine and other academic institutions — which is why university-affiliated labs are often the gold standard for this testing.
Related Reading
- Which Dog Breeds Get IVDD Most? The At-Risk Breed List
- Hansen Type I vs Type II IVDD: The Two Very Different Diseases
- Pet Insurance & IVDD: Is It Worth It for At-Risk Breeds?
Genetic testing won’t protect your dog from every disc problem, and a positive result doesn’t mean disaster is coming. What it does is give you real, specific information about your dog’s biology so you can make better decisions — about prevention, about insurance, about when to take symptoms seriously, and for breeders, about which pairings to prioritize. That’s worth something. Knowledge doesn’t remove the risk, but it does mean you’re not caught completely off guard.
Frequently Asked Questions
What does a positive CDDY result mean for my dog?
A positive CDDY result means your dog carries one or two copies of the FGF4-12 retrogene, which is strongly associated with chondrodystrophic body shape and early disc calcification. It raises the likelihood of IVDD but does not guarantee your dog will ever have a disc episode. Many CDDY-positive dogs live full lives without a single incident.
Which dog breeds should consider IVDD genetic testing?
Any chondrodystrophic breed benefits from testing, including Dachshunds, Corgis, Basset Hounds, French Bulldogs, Shih Tzus, Pekingese, Beagles, and Cocker Spaniels. Testing is especially useful for breeders selecting breeding pairs, buyers evaluating puppies, and owners who want a clearer picture of their dog’s individual risk level.
Where can I get an IVDD genetic test done?
Several university and commercial labs offer the CDDY/FGF4 test, including the UC Davis Veterinary Genetics Laboratory and Embark. Your veterinarian can submit a cheek swab sample, or you can order a kit directly from the lab. Results typically take two to four weeks.
Can genetic testing replace regular veterinary checkups for at-risk breeds?
No. Genetic testing gives you risk information, not a clean bill of health. Even a low-risk result doesn’t mean your dog is immune to disc disease. Regular vet visits, weight management, and activity modifications remain essential regardless of test results.
This guide is based on real experience and should be used alongside professional veterinary care. Always consult your veterinarian before starting any new treatment or making changes to your dog’s care plan.