Author

Stephen J. Birchard DVM, MS, Diplomate ACVS

Thursday, April 3, 2014

Are Purebred Dogs More Likely to Have Inherited Disorders? The answer may surprise you!

Prevalence of inherited disorders among mixed-breed and purebred dogs: 27,254 cases (1995–2010)
Thomas P. Bellumori, MS; Thomas R. Famula, PhD; Danika L. Bannasch, PhD, DVM; Janelle M. Belanger, MS; Anita M. Oberbauer, PhD. JAVMA, Vol 242, No. 11, June 1, 2013. Pg. 1549

Summary

In this study the authors analyzed data from dogs seen at a university veterinary teaching hospital. (University of California-Davis) The medical records were evaluated for dogs with one of 24 inherited conditions: different forms of neoplasia (hemangiosarcoma, lymphoma, mast cell tumor, osteosarcoma), aortic stenosis, dilated cardiomyopathy, hypertrophic cardiomyopathy, mitral valve dysplasia, patent ductus arteriosus, ventricular septal defect, hyperadrenocorticism, hypoadrenocorticism, hypothyroidism, elbow dysplasia, hip dysplasia, intervertebral disk disease, patellar luxation, ruptured cranial cruciate ligament, atopy, bloat, cataracts, epilepsy, lens luxation, and portosystemic shunt.

In 13 of these disorders there was no difference in prevalence between purebred and mixed breed dogs. Purebred dogs were more likely to have 10 of the inherited disorders, and mixed breed dogs were more likely to have 1 of the disorders (ruptured cranial cruciate ligament).

Disorders that were equally prevalent in purebreds and mixed breed dogs were all the neoplasms (hemangiosarcoma, lymphoma, mast cell tumor, and osteosarcoma), hypertrophic cardiomyopathy, mitral valve dysplasia, patent ductus arteriosus, ventricular septal defect, hip dysplasia, patellar luxation, hypoadrenocorticism, hyperadrenocorticism, and lens luxation.

Inherited disorders that were more common in purebred dogs were aortic stenosis, dilated cardiomyopathy, hypothyroidism, elbow dysplasia, IVDD, atopy, bloat, cataracts, epilepsy and portosystemic shunts. The only inherited disorder more common in mixed breed dogs was ruptured cranial caudal ligament. As a sidelight, mixed breed dogs were more commonly hit by a car than purebred dogs.

Commentary

The conventional wisdom is that purebred dogs are more likely to be affected by inherited disorders. In this study that was not true for all disorders, in fact less than half of the ones evaluated. Only 10 of the 24 disorders studied were more commonly found in purebred dogs, a surprising result of the research. Particularly surprising is the equal prevalence of hip dysplasia, patellar luxation, and patent ductus arteriosus between purebred and mixed breed dogs. These are all disorders that we generally think of being associated with specific pure breeds (German Shepherd-hip dyspasia, toy breeds such as miniature poodle for patellar luxation, and poodle for PDA). Hip dysplasia was equally expressed between purebred and mixed breed dogs in a previous study as well.

Dogs are thought to be descendents from just a few lineages of wolves. The authors postulate that the unexpected equal prevalence of many genetic disorders among dogs may be due to this history of domestic dogs. If true, genetic mutations would be widespread among all dog populations.

The findings of this study suggest that inherited disorders vary in their prevalence according to the disorder, not whether a dog is purebred or mixed breed. In other words, contrary to what we might think, mixed breed dogs get genetic disorders too! Hopefully studies like this will improve our understanding of genetic disorders in small animals and help devise strategies to eliminate them from future populations.

Post your thoughts about this interesting study!