CDDY info

Let’s talk about CDDY/IVDD. 
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Chondrodystrophy (CDDY) is a common body shape in many breeds and is characterized by relatively shortened legs compared to body length. Although it is also found in many breeds that aren’t necessarily short legged but also just small. I’ve been doing a ton of research on is the CDDY gene in Papillons. From my understanding, it’s a fairly new DNA test and it’s also only a linked marker test through several labs.

To reiterate, CDDY stands for chondrodystrophy and it’s a gene associated with short legs and a long back but it’s in most toy breeds as well as the low rider breeds and most bulldogs and spaniels. In some breeds it’s definitely an issue and some of the breeds with this gene are known to have back problems. While it is seen in most spaniel breeds, including Papillons, Paps and most other spaniels are not known to be riddled with back issues. Obviously they can and do pop up, especially in regard to injuries that small dogs are more prone to due to their size and fragility. 
CDDY is a fixed gene in many breeds, meaning most if not all dogs in the breed have the gene, like Toy Poodles, Beagles, Cocker Spaniels, Cavaliers, Papillons, French bulldogs, and more. 

My findings have been that somewhere around 80% or more of Papillons have at least one gene for CDDY. From the research I’ve been doing, with either one or two copies it doesn’t mean the dog will develop back problems, but that they’re at a higher risk and that risk level appears unclear. I’ve been speaking with a lot of other breeders of BorderPaps and Papillons about it and most of the Papillon people aren’t at all concerned about the gene and I haven’t seen any washing dogs from breeding because of it. It wouldn’t really be feasible to try to breed out of the Papillon population entirely because of how it would bottleneck the gene pool and raise co-efficiency of inbreeding, leading to more and other issues. The BorderPap people I’ve talked to mostly agree with me that it’s something to be aware of and worth testing for and within sport mixes, trying to avoid breeding two dogs with the gene, especially since we have Border Collies who are free from CDDY. Therefore it would be more of a problem in the multigenerational mixes. Overall, my findings have been that Paps and Pap mixes don’t have a high incidence of IVDD or back problems. But as with any dog, it’s good to be careful especially while a puppy is still growing not to do too many jumps over shoulder height, not allowing them to jump off furniture over and over, making sure they don’t get stepped on by bigger dogs or roughhoused too badly. From what I’ve found, dogs with phenotypically shorter legs and longer backs are at a higher risk of actually developing back problems - I.e. Dachshund like body types. 

Below is a list of breeds that UC Davis classifies as appropriate for testing, which you’ll see does not include Papillons. They do mention that it is not a complete list of breeds, since research on the distribution of the gene across breeds is still ongoing. 
Breeds appropriate for testing: Alpine Dachsbracke, American Cocker Spaniel, Australian Shepherd, Basset Hound, Bavarian Mountain Hound, Beagle, Bichon Frise, Boykin Spaniel, Cardigan Welsh Corgi, Cavalier King Charles Spaniel, Chesapeake Bay Retriever, Chihuahua, Chinese Crested, Clumber Spaniel, Coton de Tulear, Dachshund, Dandie Dinmont Terrier, Danish Swedish Farmdog, English Springer Spaniel, Entlebucher Mountain Dog, French Bulldog, German Hound, Havanese, Goldendoodle, Jack Russell Terrier, Labradoodle, Maltese, Pekingese, Pembroke Welsh Corgi, Pinscher (Miniature), Poodle (Miniature and Toy), Poodle (Standard), Portuguese Water Dog, Pug, Rat Terrier, Russian Tsvetnaya Bolonka, Schweizer Laufhund, Schweizerischer Niederlaufhund, Scottish Terrier, Sealyham Terrier, Shih Tzu, Skye Terrier, Yorkshire Terrier. 

Appropriate breeding decisions regarding dogs which have inherited the gene need to address both the potential loss of genetic diversity in a population which would occur if dogs with this mutation were prohibited from breeding. 

“The Fibroblast growth factor 4 (FGF4) retrogene insertion on chromosome 12 may be responsible for a portion of cases of chondrodystrophy and increased risk for Type I IVDD in certain dog populations. Dogs with one copy of this variant have modestly shortened legs, while dogs with two copies are more likely to have the characteristically short legs with a relatively long body. CDDY can be caused by other variants alone or in combination with this FGF4 retrogene. The FGF4 retrogene also increases the risk of Type I Intervertebral Disc Disease (IVDD) in a dominant fashion. This means dogs with one or two copies of this variant are at an increased risk of developing this disease. While this variant is known to increase the risk of Type I IVDD, it does not explain all cases. There are other factors that contribute to the overall risk of developing Type I IVDD, including other (unknown) genetic variants, lifestyle and other environmental factors.
It is important to understand the frequency of this variant within certain populations is very high, because certain breed standards call for a chondrodystrophic (short legs, long body) appearance. When deciding whether or not to breed a dog with this variant, we recommend considering the whole dog (rather than this one test in isolation). Other factors to consider include:
* Have any relatives of this dog shown back, neck, or neurologic problems?
* Does this dog meet the breed standard?
* Has this dog passed its breed-required health testing?
* Does this dog have the desired temperament for the breed?
* Is this dog otherwise healthy?
If all other health and temperament parameters are desired, then breeding dogs with one or two copies of the variant to dogs with no copies is a first step towards reducing the high frequency of this variant within certain breeds. Among breeds in which the frequency of this variant is high, dogs with one or two copies of this variant should not be immediately removed from the breeding population. This practice can reduce the size of the breeding population substantially, leading to other health issues associated with inbreeding and reduced genetic diversity.” - Cornell University College of Veterinary Medicine. 

“Please note that this variant is extremely common in many small and chondrodystrophic dog breeds. In these breeds, this variant may not be the strongest predictor of IVDD risk compared to other genetic or environmental factors. 
Research indicates that dogs with one or two copies of this variant have a similar risk of developing IVDD. However, there are some breeds (e.g. Beagles and Cocker Spaniels, among others) where this variant has been passed down to nearly all dogs of the breed and most do not show overt clinical signs of the disorder. This suggests that there are other genetic and environmental factors (such as weight, mobility, and family history) that contribute to an individual dog’s risk of developing clinical IVDD.” - Embark Veterinary, Inc.

To sum it up, as with many other things in dog breeding, it’s a gray area and something that should be assessed by each individual as to what their comfort levels are. It will be my goal to eventually breed out the CDDY gene but I do not plan to cull otherwise exemplary dogs from breeding due to this gene. 

Sources: UC Davis, Paw Print Genetics, Cornell University, Embark