What is Chondrodystrophy and Intervertebral Disc Disease, CDDY/IVDD, Type I IVDD
Chondrodystrophy (CDDY) refers to the "long and low" body shape characteristic of many dog breeds including Dachshunds and Corgis. Recently, a mutation was discovered that not only predicted the chondrodystrophic body shape, but increases the risk of Type I intervertebral disc disease (IVDD or "slipped disc."). A dog with one or two copies of this mutation has an increased risk of developing IVDD compared to a dog with zero copies. Its effect on body shape is slightly different--a dog with one copy of the retrogene is likely to have longer legs than a dog with two copies, but shorter legs than a dog with zero copies. We measure this result using a linkage test.
Please note that this mutation is extremely common in many small and chondrodystrophic dog breeds. In these breeds, this mutation may not be the strongest predictor of IVDD risk compared to other genetic or environmental factors; further, no genetic mutation is a guarantee of clinical disease. There is active research going in to the frequency of this mutation within particular breeds and how it impacts IVDD risk. It is likely that other genetic factors that can contribute to IVDD risk, as well as environmental factors. In addition, many chondrodystrophic dogs do NOT have this mutation--another even more common FGF4 retrogene on canine chromosome 18 also drives a chondrodyplastic body type, but is not associated with IVDD (described in Parker et al 2007).