Purebred dogs could be doctor's best friend
19:00 20 May 04
NewScientist.com news service
A study of 414 pedigree dogs from 85 breeds has uncovered some genetic surprises which could boost efforts to track down human disease genes for illnesses such as cancer, heart disease and diabetes.
Leonid Kruglyak at the Fred Hutchinson Cancer Research Center in Seattle, Washington, and his colleagues found that the breeds could be assorted into five major groups, revealing some unexpected family relationships.
For example, despite their appearance, the Sharpei and Shih Tzu turn out to be close relatives of the Siberian Husky and Alaskan Malamute. And all four belong to the group most closely related to the ancestor of all dogs, the wolf.
Each breed was also defined by a surprisingly precise genetic signature. By studying a few pieces of DNA from a purebred dog, the researchers were able to assign its breed with 99 per cent accuracy.
"This should help people hunting for disease genes to find them more efficiently and give them new ways to look," says Kruglyak. Knowing the relationship between breeds, for instance, will allow researchers to group disease data from closely related breeds, giving gene hunts more statistical power.
To gather samples for the study, the researchers enlisted the help of individual breeders and the American Kennel Club, which maintains a huge registry of dogs and their breeders. Cheek cells were swabbed from each animal's mouth, DNA extracted and analysed for microsatellites, small unique DNA sequences used to track genes. Genetic analysis then revealed the familial relationship of the breeds.
While some relationships came as a surprise, many of the groupings were more intuitive given the appearance of the dogs or the roles they play. The Bull Mastiff and Bulldog were in one group, while herding dogs like the Collie and Shetland Sheepdog were in another.
The remarkable overall genetic distinctiveness of the breeds is hard to explain, given that formal dog breeding standards were only introduced 150 years ago. "That's about 40 dog generations, not very long at all in evolutionary terms," says Kruglyak.
He theorises that many factors might have unintentionally driven a quick
genetic separation of the breeds. Widespread breeding of prized animals
would have widely dispersed a few genetic types, for example. And when
a particular breed fell out of fashion, the whole population many might
have dwindled down to very few animals, limiting the gene pool.
Whatever the reason, Jaime Modiano of the University of Colorado Health Sciences Center in Denver points out that this newly discovered genetic structure is yet another factor that makes the purebred dog such a valuable tool for human disease research.
Because owners lavish veterinary care on their pets, knowledge of natural dog disease rivals that of human diseases. The dog genome is also expected to be published in the summer of 2004, which will make comparisons between dog and human genes far easier.
However, for a disease such as cancer, genes are only thought to be half of the puzzle - environment also plays a role. And being the close companion of humans for millennia has exposed dogs to many of the same chemicals, foods, and lifestyles.
"Dogs pretty much do everything we do, except drive and play the piano," says Modiano.
Journal reference: Science (vol 304, p 1160)