Chondrodystrophy (CDDY) and Intervertebral Disc Disease (IVDD) Risk

Chondrodystrophy (CDDY) is a form of skeletal dysplasia which affects the development of cartilage and bone growth in a number of dog breeds. The associated CDDY genetic variant is an FGF4-retrogene insertion on dog chromosome 12, discovered by researchers in the Bannasch Laboratory at the University of California, Davis (Brown et al. 2017), and should not be confused with the FGF4-retrogene insertion on dog chromosome 18 (Parker et al. 2017), associated with a short-legged phenotype known as chondrodysplasia (CDPA). In dogs with CDDY, disproportionate growth (short limbs, normal sized body and head) can be observed as early as one week of age. CDDY follows a semi-dominant mode of inheritance. This means dogs with one copy of the genetic variant typically have some shortening of their legs, whereas dogs with two copies will show a more obvious shortening. Although not necessarily directly associated with CDDY, valgus limb deformities may be observed during physical examination of some dogs. However, affected dogs are more likely to experience premature degeneration and calcification of the intervertebral discs, a process also known as intervertebral disc disease (IVDD). Dogs with IVDD secondary to this genetic variant have an increased risk of intervertebral disc herniation (IVDH), consistent with Hansen Type I. The risk of developing IVDH follows a dominant mode of inheritance, meaning only one copy of this variant is needed to consider a dog predisposed for disc herniation. Age of onset of disc herniation appears to vary considerably between breeds, with the median age of dogs presenting for surgery varying from 3 years to 10 years. However, please note this variant is a risk factor and some dogs with one, or even two copies, of this variant may not go on to show signs of disc disease. It is worth clarifying that if disc herniation does not occur dorsally, a dog may appear asymptomatic as the spinal cord is less likely to be compressed. Additionally, not all dogs affected by IVDD have the FGF4-retrogene insertion found on chromosome 12, indicating additional genetic causes remain to be discovered.

While it is not possible to completely prevent the development of IVDD in individuals who are predisposed, maintaining a lean body weight and healthy musculature are strongly advised for any dog that is at risk of disc herniation during their lifetime. Maintaining a healthy weight is important to prevent undue strain on the spine and other joints. And, regular exercise can help to build strong back muscles to support the spine. Further actions that may help reduce the risk of disc herniation include restriction of high-impact activities that could cause twisting of or compression of the spine. Restriction of jumping remains controversial for dogs with IVDD; however, the use of ramps in older pets to get on/off furniture may aid in their independence as they lose joint flexibility. For dogs who experience disc herniation, medical management is indicated in mild to moderate cases and typically includes medication for pain and inflammation along with strict activity restriction. In severe cases, surgical intervention is often warranted.

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This variant is considered a risk factor for Chondrodystrophy (CDDY) and Intervertebral Disc Disease (IVDD), and dogs with one or two copies of the variant are at increased risk. However not all dogs with one or two copies of this variant will show signs of disc disease. Use of dogs with one or two copies of the CDDY and IVDD variant should be critically considered, as there is a risk that the resulting litter will contain affected puppies. For example, if a dog with one copy of the CDDY and IVDD variant is bred with a clear dog with no copies of the CDDY and IVDD variant, about half of the puppies will have one copy and half will have no copies of the CDDY and IVDD variant. Some breeds carry the variant at such a high rate that breeding dogs with one copy of the disorder is unavoidable. In such cases, mate selection should be planned to slowly reduce the frequency of the variant within the breed over time if possible. In breeds where both FGF4 retrogenes are present and a short stature is desirable, breeders can select for dogs positive for the CDPA (chromosome 18) variant, and against dogs with the CDDY (chromosome 12) variant to maintain breed-specific leg length. Please note: It is possible that clinical signs similar to the ones associated with the CDDY and IVDD variant could develop due to a different genetic or clinical cause.