CDDY in dogs: what chondrodystrophy means for the back and discs

CDDY in dogs stands for chondrodystrophy, an inherited peculiarity in the genome. Dogs with CDDY carry an extra copy of the FGF4 gene on chromosome 12. It contributes to shorter legs, but above all the intervertebral discs age earlier and calcify more often. This increases the risk of a herniated disc, even in young dogs. Not every dog with CDDY develops problems, but it is worth knowing the risk and protecting the back in everyday life.

What is CDDY in dogs?

In some dogs, an extra copy of the FGF4 gene became established in the genome over the course of breeding history. If it lies on chromosome 12, it is called CDDY. It acts dominantly: even one copy is enough to increase the risk of disc problems. A similar copy on chromosome 18, often called CDPA, is mainly linked to very short legs and plays only a small role for the discs.

What CDDY means for the discs

The intervertebral discs sit between the vertebrae and cushion movement. In dogs with CDDY, they lose their elasticity early and calcify. In one study, calcified discs were seen on X-rays in 85 % of dogs with two CDDY copies, 64 % with one copy and 19 % without CDDY. Dogs with CDDY needed surgery for a herniated disc at a younger age on average. In mixed breeds, even a single copy was linked to a clearly higher risk of such surgery (in the study, an odds ratio of around 18).

Which breeds carry CDDY?

What does a genetic test show?

The values in the table come from samples in a study. 100 % means that all dogs of the breed examined carried two copies. A genetic test from a saliva or blood sample shows whether your dog carries no, one or two copies of the CDDY variant. The result is not a diagnosis but an indication of risk: dogs with CDDY can stay free of a herniated disc all their lives, and dogs without CDDY can still get one. For owners, the result helps them to be more alert. For breeding, it is particularly important.

CDDY and breeding

The researchers recommend favouring dogs with fewer CDDY copies in breeding. In breeds where the variant is rare, it can be reduced in a targeted way. In breeds where almost all dogs carry it, genetic tests can help to gradually use dogs with only one copy and later dogs without CDDY. If you ask a breeder about a puppy, also ask about the parents’ CDDY results.

Emergency: when to go to the vet immediately

• Pain: Your dog holds his back or neck stiffly, cries out when lifted or doesn’t want to move.
• Gait: He walks unsteadily, knuckles over on his paws or drags his hind legs.
• Bladder and bowel: He can no longer hold his urine or can’t pass it.

How to protect the back in everyday life

• Keep his weight healthy: Every extra kilo puts additional strain on the spine.
• Avoid jumping: Ramps for the sofa and car spare the back hard landings.
• Exercise evenly: Regular, calm walks are better than wild play with abrupt turns.
• Strengthen muscles: Targeted exercises, for example with a canine physiotherapist, can strengthen the back muscles.
• Non-slip floors: Rugs on smooth floors prevent slipping.

Frequently asked questions

Source

• Batcher K. et al.: Phenotypic Effects of FGF4 Retrogenes on Intervertebral Disc Disease in Dogs, Genes 2019.

CDDY is not a verdict, but it is a good reason to look after your dog’s back. If you know the risk, you’ll spot warning signs earlier and can cushion a lot in everyday life.

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