Researchers Consider Breed Predisposition to Cancer
Used with permission from Today's Breeder, Nestle Purina PetCare Company.

Canine cancer is a complex disease involving many genes. Once it is detected clinically, it may consist of many cells with dozens or possibly hundreds of abnormalities. Unfortunately, it also is the leading cause of disease-related death in dogs. Both genetic and environmental factors are believed to effect cancer, thus researchers are focusing on how these factors influence the cellular and molecular changes in cancer. Canine cancer researcher Jaime Modiano of the University of Colorado at Denver and Health Sciences Center points out, “It is not possible to breed out a cancer gene and eliminate disease, but It may be possible to identify risk factors and breed them out.”

Genetic Relationships
Seeking to understand what breeds are closely related so they could concentrate on a subset of breeds when studying a particular disease or cancer, scientists conducted a genetic analysis of 414 dogs representing 85 breeds recognized by the American Kennel Club. “If we were to study a disease that is present in the Mastiff, we would hypothesize that the same disease might occur in the Bull Mastiff, Boxer, Bulldog, Miniature Bull Terrier and Rottweiler because of the same ancient mutation they carry,” says Elaine Ostrander, PH.D., chief of the Cancer Genetics Branch at the National Human Genome Research Institute.

“Studying multiple breeds simultaneously gives us much greater statistical power for finding any particular gene.” She says. “an accurate understanding of the genetic relationships among breeds lays the foundation for studies aimed at uncovering the complex basis of breed differences in morphology, behavior and disease susceptibility.”

Applying microsatellite typing, combined with phylogenetic analysis and modern clustering methods, to the breeds in the study, the scientists were able to define four related groups of breeds. “Comparing the genes of dogs and wolves, we concluded that a group of ancient dog types split off first,” Ostrander says.

“Later, the majority of dogs evolved into three clusters – hunters, herders and guard dogs – largely as a result of breeding programs.”

The ancient dog types of Asian and African origin were the first to develop. This includes the Basenji, Saluki, Afghan Hound, Lhasa Apso, Tibetan Terrier, Chow Chow, Pekingese, Sharpei, Akita, Shiba Inu, Alaskan Malamute, Siberian Husky, and Samoyed. After the ancient breeds, European breeding programs and breed clubs in the 1800s created dogs that were hunters, herders or guard dogs. Guard dogs were Mastiff-like breeds, such as boxers, Bulldogs and Rottweilers. Herding breeds included Shetland Sheepdogs and Collies. Hunters were breeds developed for various aspects of hunting.

The results of the study were published in Science magazine in may 2004 in an article titles “Genetic Structure of the Purebred domestic Dog.” The findings provided an independent classification of dogs based on genetic variation. This information has contributed to studies of canine disease and cancer including the lymphoma and osteosarcoma research covered in this article, as researchers search for susceptibility in families or breeds of dogs.