Understanding the genetics of IVDD – let’s not get too excited (just yet)!

Spine_X-ray2University of California, Davis, researchers have revealed the discovery of a genetic mutation across breeds that is responsible for chondrodystrophy (the skeletal disorder leading to shorter legs and abnormal intervertebral discs) in a study published in the Proceedings of the National Academy of Sciences. [UCD Press Release]
The paper says there are two FGF4 retrogenes on chromosomes 12 and 18. The one on 18 causes dwarfism (CDPA), the one on 12 is associated with dwarfism and IVDD (CDDY). The paper suggests 100% of Dachshunds are homozygous for the 18 version and the key question is what proportion have a copy of the 12 version. If 100% of Dachshunds have the CDDY version, then this will be of no use to us in breeding away from IVDD.

The Mogensen study of 2011 suggests there may well be differences in frequency of the CDDY version because they found variations in calcification risk associated with a Chromosome 12 locus in a sample of 94 Dachshunds.

We do have to be careful in interpreting this UCD paper because the Supplemental Information shows that only 3 Dachshund IVDD cases were in their sample. All the IVDD cases from a number of breeds were diagnosed based on calcifications on x-rays and/or surgery.

We really need CDDY frequency data from a well-defined, large sample of Dachshund cases and controls. If there is a variation in the CDDY frequency in Dachshunds so that they can be identified as Clear, Carrier or Affected, that would suggest we can breed away from IVDD. It all depends on how widespread the CDDY variant is.
A viable breeding strategy will be dependent on what proportion are “Clear” of the IVDD risk retrogene. Breeding to a small number of Clear dogs could be a genetic diversity disaster. We need more data before we can celebrate the value of this latest research.
The UCD Veterinary Genetics Laboratory is offering a combined test for CDDY and CDPA. The Breed Council’s Health Committee is currently seeking further information on the research and the test. At the moment, they cannot make a recommendation on this test to breeders and advice therefore remains that the X-ray screening programme is the preferred option.
Download the UCD paper (pdf)
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