Summary of a Sponsored study of BTCA with UC Davis Study

The Biewer Terrier Club of America (“BTCA’) sponsored a study done by the University of California, Davis (“UC Davis”) to test for the percentage of two genetic mutations as part of our ongoing role supporting health and research in our breed. The BTCA wishes to give a summary of the current findings and possible considerations for Biewer Terrier breeders and other owners.

This sponsored study consisted of testing of up to 100 Biewer Terriers for the frequency of the chondrodystrophy (“CDDY”) and chondrodysplasia (“CDPA”) genetic changes. The CDPA is a dominant mutation, while CDDY is a semi-dominant mutation for the short-legged phenotype. One or the other, or both, are found in many toy breeds and others such as Dachshunds, Basset Hounds, and Pembroke Welsh Corgis. In recent studies that led to the discovery of this CDDY mutation, also found it to be a dominant gene as it relates to an increased risk for herniated spinal discs. It can be found in canines in 1 or 2 copies. In 2017, researchers at UC Davis found this CDDY mutation on chromosome 12, when looking for the genetic cause of intervertebral disc disease (“IVDD”). CDDY is an additional copy of the same retrogene that causes CDPA on chromosome 18, but its location changes some of its actions. A follow-up study found CDDY produces an increased risk for disc herniation for carriers of this mutation over dogs that were clear.

Although, other studies have shown a correlation between 1 or 2 copies of CDDY as increasing the risk for disc herniation in the breeds in their study; there was no Biewer Terrier in the UC Davis studies. As this mutation was only recently identified, there are no long term studies looking at the definite likelihood of developing disc problems in Biewer Terriers or other breeds. The specific risk in our breed is unknown.

In this BTCA study, 91 Biewer Terriers were used for analysis. UC Davis compared the number of dogs with 1 or 2 copies of CDDY to those who did not have the mutation to determine the allele frequency of the mutation in Biewer Terriers. In our BTCA sponsored study, the presence of CDDY was calculated to be 12.65%. This gives the Biewer Terrier an allele frequency of approximately 0.13. The allele frequency for other breeds with limited or large numbers is available in the UC Davis study.

When reviewing our 0.13 allele frequency of CDDY and comparing it with a chart of the other breeds with 1 or 2 copies studied by UC Davis, Biewer Terriers are one of the lowest. Also, many of the other breeds had fewer than 10 dogs in their studies. Thus, the breed data is still emerging on the allele frequency and may affect the calculated relative risk for those breeds. (https://vgl.ucdavis.edu/test/cddy-cdpa” https://vgl.ucdavis.edu/test/cddy-cdpa).

Nonetheless, as the CDDY has been shown in some breeds to have an increased risk for IVDD, the BTCA suggests that all breeders use their best judgment in making decisions for both testing and mating. This may include testing for the CDDY and the decision of selecting a mate clear of CDDY when breeding to a Biewer Terrier who has one or two copies of the CDDY mutation.
Please direct all questions for the study to a member of the BTCA Board or the BTCA Health Chair.