October 19, 2015

The challenges of pedigree dog health: approaches to combating inherited disease

In this article, the authors discuss the problems facing pedigree dogs due to inbreeding. Dogs have experienced two major population events, called "bottleneck events," where the populations have suffered from a loss of diversity: the first being domestication and the second being breed formation. As certain dog breeds have become more popular, those breeds fall victim to inbreeding (due to desire for certain physiological/aesthetic characteristics) and from that suffer a loss of genetic diversity, which sometimes can lead to greater inheritability of genetic disorders. (*Sometimes is used because there is not always a direct association/correlation beteween loss of diverisity and heritable diseases as demonstrated by a recent Swedish study).    

For example, brachycephalic airway syndrome (BAS) is a genetic disorder that restricts the airway and affects breathing, ability to exercise, overheating and can, ultimately, cause death in certain dog breeds that have been bred for their flat faces, like pugs. These dog's faces are flat as the result of a flat skull, which can cause medical problems other than those that result in respiratory symptoms: increased tendency of eye trauma, ulceration, and proptosis due to the shallowness of their eye sockets and increased tendency of cleft pallets. The dogs also have smaller body sizes than usual due to selective breeding, and, as a result, have inherited problems with growth hormones.

Designer dogs, like the puggle (pug and beagle), are also victim to hereditary problems. The common misconception is that these designer dogs have less problems, but they can have as many or more genetic problems due to shared genetic abnormalities between the crossed breeds. The authors of the article suggest ending this practice, especially considering the historical impact of human selection in dog breeds.

The current methods of managing these condtions includes many efforts by the English Kennel Club (EKC). These current methods include breeding strategies and screening schemes. The breeding strategies incorporate genetic testing into the standards breeders must follow. For breeders to begin breeding pedigree dogs, they must screen their dogs (both male and female) for DNA diseases and their dogs must be examined by a veternarian for symptoms of these diseases. These methods have significantly reduced the prevelance of genetic diseases in pedigree dogs, but have made no difference in efforts to eliminate these diseases, especially since the tests are not mandatory for all breeds. The authors propose several strategies of combating these heritable disease, including preventive measures for breeders like free diagnostic screening and genetic testing days. They also suggest breeding dogs from similar, but different, breeds to "breed away" from disease. 

Farrell, Lindsay L., Jeffrey  J. Schoenebeck, Pamela Wiener, Dylan N. Clements, and Kim M. Summers, 2015. "The challenges of pedigree dog health: approaches to combating inherited disease." Canine Genetics and Epidemiology, 2:3.