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Dogs May Offer Insights Into Disease in Humans

Posted on: Friday, 21 May 2004, 06:00 CDT

By Randy Dotinga, HealthDay Reporter

HealthDayNews -- A team of American researchers has identified the genetic differences between dozens of purebred dog breeds, setting the stage for a greater understanding of the countless diseases that afflict both man and his best friend.

"Dogs are probably the closest species to humans that we have to work with," said Deborah Lynch, president of the Canine Studies Institute, who helped the researchers with the study. "They seem to mirror our diseases, and more than any other species they live with us and eat our food, sharing the environment, too."

Led by scientists at the Fred Hutchinson Cancer Research Center in Seattle, researchers gathered DNA from 414 dogs representing 85 purebred breeds. Rather than rely on hard-to-obtain blood tests, they asked owners to swab the cheeks of their pooches.

Ideally, purebred dogs are only bred with canines of their own kind. Dog owners have kept track of lineages since at least the 19th century.

The findings appear in the May 21 issue of Science.

The study authors report they've identified four mega-breeds of dog, which they called "clusters." Dogs in the various groups appear to have evolved at about the same time.

For example, a cluster of dogs descended from ancient Asia and Africa -- including the Shar-Pei, Shih Tzu, Akita and Siberian husky, among others -- appear to be closest in ancestry to the wolf. Dogs thought to have been around for thousands of years -- including the Ibizan hound -- didn't appear in the cluster of old-timers, suggesting that perhaps their breeds were recreated in later years after the original breed died out.

The other three clusters of dogs are the mastiff-types (such as the Bulldog and Rottweiler), the herding dogs (sheepdogs and the collie), and, finally, the terrier and scent dogs (bloodhounds, Scottish terriers and many more).

Besides answering questions about the most diverse mammals in the world -- there are some 400 breeds of canine familiaris -- dog researchers say the findings will help scientists understand the workings of disease.

More than 350 diseases strike dogs, including many that are also found in humans. Some ailments plague specific breeds, such as deafness among Dalmatians, Addison's disease (a disruption of hormone production) in Portuguese water dogs, and glaucoma in basset hounds. Nine of the 10 most common dog diseases strike humans, too, including cancer, epilepsy, autoimmune disorders and heart ailments, the researchers said. (The one exception is a dog-specific disease called bloat.)

Lynch said the findings about the similarities and differences between breeds will help scientists pinpoint specific genes that cause disease.

If cancer is common in a particular breed, for example, scientists could analyze another breed with the same tendency and look for shared genes, she said. Already, scientists have made inroads on this front by mapping much of the genome -- the genetic blueprint -- of the boxer and the poodle.

"The most important thing will be when dogs are used as models of human disease," said Gordon Lark, an emeritus professor of biology at the University of Utah, who studies the genetics of Portuguese water dogs.

But does that mean dogs will end up becoming popular laboratory test subjects, such as mice and rats, doomed to death in a cage? Beagles, after all, are already used in laboratory research.

Dog researchers -- many of whom are canine lovers themselves -- say they hope scientists will be able to make medical breakthroughs without having to sacrifice potential pets in the process. Ideally, dogs would be able to fulfill their age-old obligations to their owners by contributing DNA samples from the safety of their homes.

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On the Net:

American Veterinary Medical Association

University of California, Davis

Fred Hutchinson Cancer Research Center

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