The Embark for Breeders Dog DNA test now includes the trait test for Chondrodysplasia (CDPA) to help breeders make informed decisions for their breeding programs.
What is Chondrodysplasia (CDPA)?
CDPA is a trait resulting in the short-legged appearance consistent with the breed standard of many breeds, such as the Dachshund, Basset Hound, and Corgi. It is considered a normal finding in these (and other similarly shaped) breeds, with most individuals carrying one or two copies of the variant to give them their characteristic short stature.
CDPA is considered a trait in dogs and is not generally associated with specific health concerns. However, in some breeds with a taller breed standard height, CDPA may result in individual dogs that are too short to meet height requirements.
How is CDPA inherited?
CDPA is inherited in an incompletely dominant fashion. This means that dogs with one copy of the CDPA variant will display a moderate decrease in height compared to dogs with two copies of the variant (largest decrease in leg length) and dogs with no copies (unaffected/normal leg length).
How is CDPA Related to Chondrodystrophy (CDDY)?
Along with CDPA, CDDY has played a historically important role in creating breeds with a short-legged appearance, as CDDY also decreases leg length. In fact, most breeds with extremely short legs inherit both of the genetic variants associated with these traits.
Other short-legged breeds may only have one of these variants or neither variant. The biological impacts of these variants result in alterations to bone growth and, subsequently, shorter limbs.
However, CDPA has a much greater impact on decreasing leg length than CDDY (about 2 to 8 times greater decrease depending on breed).Both traits are caused by a similar type of genetic variant known as an FGF4 retrogene.
A retrogene is a copied gene or section of a gene that becomes inserted into an aberrant genome location. In the case of CDDY, a copied version of the FGF4 gene has been inserted on canine chromosome 12. For CDPA, a similar insertion is found on canine chromosome 18.
How can CDPA test results be used in a breeding program along with CDDY results?
There are multiple ways in which the CDPA test results can be used for breeding, and the specific use will depend upon the frequency of the CDDY and CDPA variants in the breed being tested and the breed standard height of that breed.
Unfortunately, CDDY (but not CDPA) is also associated with an increased risk of the disease, Type I Intervertebral Disc Disease (IVDD). For this reason, when possible, it is ideal to eliminate the CDDY variant from bloodlines through selective breeding to decrease IVDD risk.
However, in some breeds, this may not be possible without outcrossing because nearly 100% of individuals from some breeds inherit two copies of the CDDY variant. In addition, in breeds with a short breed standard height, it may be important to maintain (or select for) the CDPA variant to ensure this appearance.
For example, In some breeds like the Miniature Poodle, the CDDY and CDPA variants are both found in a relatively low frequency compared to other breeds. Therefore, many miniature poodles have fewer than two copies of both variants. This is convenient for miniature poodle breeders because this means that they have the ability to eliminate CDDY from their bloodlines through selective breeding to decrease IVDD risk.
At the same time, Miniature Poodle breeders can select the appropriate number of copies of the CDPA variant to maintain a breed-specific height in their bloodline. This same technique could be used for any other breed in which individuals have fewer than two copies of these variants. The number of CDPA copies necessary for the ideal height may vary by breed and bloodline. In breeds for which all individuals have two copies of CDPA, only the CDDY variant would need to be considered when breeding, and vice versa.
Given that CDDY is associated with an increased risk of IVDD, it may be tempting for breeders to eliminate dogs with this variant from breeding consideration. However, given the high frequency of this variant in many breeds, this technique may result in massive losses of genetic diversity within a breed.
Low genetic diversity has been associated with various health concerns, including increased incidence of recessive genetic diseases, poor fertility, small litter sizes, and decreased lifespan. Therefore, it may be safer to slowly eliminate the CDDY variant from bloodlines over multiple generations by breeding dogs with the CDDY variant to dogs that are clear of it. Once clear puppies are achieved, they can be kept for future breeding.
What breeds are affected?
The CDPA variant can be identified in nearly all breeds with an extremely short-legged appearance, including Dachshunds, Corgis, Basset Hounds, Pekingese, Dandie Dinmont Terriers, and others.
In addition, other breeds with less extreme alterations to leg length have also been identified to inherit the CDPA at various frequencies, including Norwich Terriers, West Highland White Terriers, Scottish Terriers, Miniature Poodles, and others.
Ready to start your dog DNA journey with an Embark for Breeders Dog DNA Test? Do you have questions about CDPA? Then schedule a call with Embark’s Veterinary Geneticist, Casey Carl, DVM, to learn more about this trait.
