In October 2017, University of California, Davis, researchers 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. We reported this and their claim to have developed a DNA test for IVDD. At the time, we were rather concerned that, although a potentially exciting development, the conclusions were based on analysis of a very small number of Dachshund DNA samples.
We have been working with the Animal Health Trust on the genetics of IVDD and UCD generously agreed to screen a set of samples which we had collected for Dr. Cathryn Mellersh in the UK. These comprised UK dogs aged 4-7 who had suffered IVDD herniations and dogs over the age of 10 with no clinical history of IVDD symptoms. 144 samples were sent, covering Smooth, Long and Wire coats in both Standard and Miniature sizes.
These samples were all genotyped for both FGF4 retrogenes (CFA12 and CFA18) and unfortunately all samples were homozygous for both loci. We had hoped that the Wirehaired dogs might be variable at least (based on experience from other genetic studies), but that isn’t the case.
So this means, sadly, that neither of these loci can be selected against to reduce the prevalence of IVDD, in UK Dachshunds at least.
These data also indicate that all the dogs we tested are homozygous for both of these risk factors. The fact that not all of these dogs had developed IVDD means either (i) environmental factors account for the ‘missing risk’, or (ii) that there are additional genetic risk factors that have yet to be identified. Or a mixture of (i) and (ii).
These findings reinforce those of our Danish colleagues who genotyped a similar sized sample of dogs that had (a) low calcification screening scores and (b) high scores. They found very few dogs without the mutation on CFA12.
The conclusions from the AHT samples and Danish samples mean that the UCD "test" cannot be used to screen against IVDD and our advice remains that X-ray screening is the only viable test available currently.
We are grateful to Dr. Cathryn Mellersh at the AHT and to Dr. Danika Bannasch at UCD for their support.