The science, stated plainly
What CDDY actually is. CDDY refers to a small genetic marker — an FGF4 retrogene on canine chromosome 12. It does two separate things: it modestly reduces a dog’s body size, and in certain breeds it is treated as a risk factor for Type I intervertebral disc disease (IVDD). It is important to understand from the start that it is a risk marker, not a diagnosis, and that its two effects — size and disc risk — do not carry equal weight in every breed.
It is part of why Toy and Miniature Poodles are small. Because this marker reduces size, it became common in the small Poodle varieties as breeders selected, over many generations, for smaller and smaller dogs. The marker simply came along with small size. This is why the large majority of Toy and Miniature Poodles carry one or two copies, while Standard Poodles essentially do not carry it at all. In other words, its high frequency in small Poodles is a direct reflection of their size — not a sign of a sick population.
Which breeds this disc disease is actually established in. The clinical link between this marker and disc disease was identified and documented in chondrodystrophic breeds — the short-legged, long-backed dogs built for it, with the Dachshund as the textbook example, along with breeds like the French Bulldog and Beagle. (It is worth noting that the gene responsible for the classic short “Dachshund legs” — called CDPA, on a different chromosome — is a separate marker from the disc-related CDDY. They are often confused, but they are not the same thing.) The point that matters for our breed: a Toy Poodle is not built like a Dachshund. It does not have the elongated spine and dramatically shortened legs that place mechanical stress on the discs, and body conformation is a recognized, independent factor in whether disc disease ever develops.
What has not been found.
To date, there is no published scientific study that has examined or demonstrated clinical disc disease caused by this marker in Toy Poodles specifically — in dogs carrying one copy or two. The marker’s effect on disc disease has been studied in short-legged breeds and extrapolated outward; it has never been measured within the Toy Poodle as its own population. The research designed to answer that exact question is still ongoing and has not reported results. On top of this, even in the breeds where it has been studied, the marker shows incomplete penetrance — meaning that carrying it, including carrying two copies, does not mean a dog will develop disc disease. Many never do.
The short version: this is a size-linked marker that is extremely common in small Poodles precisely because it makes them small; its disc-disease relevance is established in short-legged breeds built nothing like a Poodle; and it has never been shown to cause disc disease in Toy Poodles themselves.
Our position as an international breeding program
The following reflects the professional experience and breeding philosophy of Fancy Pets Planet.
Our program is built on an international foundation — renowned European, Asian, and Eastern European champion import lineage. Working at that level, across those circles, gives us a particular perspective on this test: outside the United States, it is rarely run and, frankly, rarely even discussed. Established breeders across Europe, Asia, and Eastern Europe concentrate on the conditions with proven, breed-specific relevance to Poodles — eyes (PRA), neurological (DM), clotting (von Willebrand) — alongside structure, temperament, and genetic diversity. CDDY testing is, in practice, a largely US-based test. We test for it and disclose it regardless, so our clients always have the complete picture, but we view it in the proper context.
That context includes two realities that matter enormously for a serious small-Poodle program:
The gene pool. Because the large majority of Toy and Miniature Poodles carry this marker, breeding only “clear” dogs would shrink the available gene pool dramatically. Selecting hard against a marker that most of the breed carries does far more damage to genetic health — the real foundation of a sound, resilient line — than it could ever prevent.
Size. Since this marker is part of what makes small Poodles small, the dogs that test clear of it tend to be the larger ones. Breeding exclusively for clears therefore pushes a program steadily away from true Toy size — the opposite of what families seeking a genuinely small Poodle are looking for.
And most important of all is what I have actually seen with my own eyes. In over 13 years of working with this breed, across more than 1,000 dogs and clients, I have never once — not a single time — seen this condition develop in any Poodle carrying two copies. That is a longer and closer record than any single lab result, and it is the real-world experience behind the position I take.
For all of these reasons, I do not breed this marker out. My European and Asian champion import lines may carry one or two copies of CDDY, and that is a deliberate, informed decision made to protect genetic diversity, preserve correct Toy size, and keep this breeding program grounded in proven science and decades of hands-on experience — not in trends.
References
- Brown EA, Dickinson PJ, Mansour T, et al. FGF4 retrogene on CFA12 is responsible for chondrodystrophy and intervertebral disc disease in dogs. PNAS, 2017.
- Batcher K, Dickinson P, Giuffrida M, et al. Phenotypic Effects of FGF4 Retrogenes on Intervertebral Disc Disease in Dogs. Genes, 2019.
- Bannasch D, Batcher K, Leuthard F, et al. The Effects of FGF4 Retrogenes on Canine Morphology. Genes, 2022.
- Murphy BG, Dickinson P, Marcellin-Little DJ, et al. Pathologic Features of the Intervertebral Disc in Young Nova Scotia Duck Tolling Retrievers Confirms Chondrodystrophy. 2019.
- Dickinson PJ, Bannasch DL. Current Understanding of the Genetics of Intervertebral Disc Degeneration. Frontiers in Veterinary Science, 2020.
- Parker HG, VonHoldt BM, Quignon P, et al. An expressed FGF4 retrogene is associated with breed-defining chondrodysplasia in domestic dogs. Science, 2009.
- University of California, Davis — Veterinary Genetics Laboratory: CDDY/CDPA test information and chondrodystrophy breeding guidance.