Cranial cruciate ligament rupture (CCLR) is a leading cause of pelvic limb lameness in dogs. About 6% of Labs suffer from this orthopedic problem and since this breed is one of the most popular in the U.S., Michael Conzemius, DVM, PhD, DACVS, and Molly McCue, DVM, MS, PhD, DACVIM, with the University of Minnesota College of Veterinary Medicine decided to collaborate on a study to determine the disease’s heritability in Labrador Retrievers and they wanted to measure the extent to which CCLR is associated with genetics in this breed.
Cruciate ligaments, connecting the femur to the tibia bones, are called cranial and caudal in quadrupeds, such a dogs; the cranial cruciate ligament (CCL) is analogous to the anterior cruciate ligament (ACL) in humans. These ligaments are prone to rupture, in humans, dogs, horses and, in other species.
Previous work has shown that approximately 2.5% of dogs are affected with at least one CCLR, and various factors including breed, sex, age and sterilization status—including age at sterilization—have some effect on the likelihood of experiencing a CCLR (Witsberger et al. 2008; Simpson et al. 2019).
While this condition is mainly found in large and giant breeds of dogs, it has been noted that it has a low incident rate in Greyhounds—a large-sized breed—so this has lead researchers to theorize that there is a genetic influence to the occurrence of CCLR.
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The researchers explained that, interestingly, in most cases with dogs, “CCLR isn’t a contact injury or due to acute trauma. This has led to various causal theories: degenerative processes may be occurring within the ligament; there exists an inability to repair damaged tissue at a typical rate; or defects exist within the dog’s general conformation (Buote et al. 2009; Muir et al. 2011).”
The methodology of this study has proven effective in horses, and this was the first study to use these techniques to estimate heritability in dogs with CCLR. The scientists found relatively high heritability for CCLR in Labrador Retrievers, which indicates that genetics contribute substantially to the disease’s prevalence in the breed.
These findings should help get clinicians one step closer to a genetic test for earlier diagnosis and treatment. However, heritability estimates do not pinpoint the genes involved, so the scientists say future studies should focus on determining which genetic mutations specifically increase the risk for CCLR in this breed.
As Michael Conzemius, the study’s co-author noted, “This is an extension of research that we began nearly 20 years ago in an effort to establish the role of genetics in this disease that is exceptionally common in some breeds of dogs. Our long-term goal has always been identifying mechanisms to decrease the frequency of cranial cruciate ligament disease. We plan to continue this work and hopefully it will contribute to a functional genetic test.”
This research was funded by the National Institutes of Health (K01‐OD027051), Veterinary Orthopedic Society, Tata Group Endowment at the University of Minnesota, and the Bernice Barbour Foundation.