Eight years have passed since Gordon Lark’s beloved Portuguese water dog Georgie developed Addison’s disease, a hormone disorder that usually occurs when the immune system attacks the adrenal glands. Since Georgie’s death, Lark, a Distinguished Professor Emeritus of biology at the University of Utah, has worked with biological information and pedigrees received from hundreds of people who own Portuguese water dogs in a novel project named after his adored pet.
Supplied with X rays and blood samples taken by veterinarians at the request of dog owners—and with a database of pedigrees of the entire breed back to its founders—Lark and his colleagues have been comparing the genes of Portuguese water dogs with their physical development, appearance and behavior.
Lark’s initial studies successfully located several combinations of genes that control distinct bone sizes and shapes. For example, one set of genes dictates specific head and limb sizes. Dogs with big heads have shorter, thicker legs, like bulldogs. Dogs with thinner heads have long, slender legs, like greyhounds.
“These are biomechanical tradeoffs,” Lark says. “Functionally, it makes tremendous sense. If you’re a runner like a greyhound, you want a streamlined head. So your skull will be small relative to the body. If you’re a pit bull, you’re more like a lion, mainly because you have tremendous jaw muscles. You want power in your legs if you’re defending your territory. You want thick legs that are strong.”
At about 50 pounds, a Portuguese water dog is a medium-sized, average-bodied dog. “But the interesting thing is, it still has genes that move along these extremes,” Lark says, “so you can change the body in either direction.”
Lark also has done interesting work on Addison’s disease, demonstrating the complexity of the genetics of the disorder that killed Georgie, and suggesting that certain immune-system boosters commonly found in canine vaccines may interfere permanently with Portuguese water dogs’ immune systems and trigger the onset of Addison’s. Lark also is looking for other environmental factors that may trigger Addison’s in dogs. To do so, he is collecting diaries kept by pet owners who record the life histories of dogs whose siblings or parents developed Addison’s disease.
“The time and effort that this [diary keeping] requires is more than repaid by the value of this information and the increase in bonding that the owner acquires from such an intimate knowledge of the dog,” Lark notes in the official project guidelines.
Another study from Lark’s lab appeared recently in the American Journal of Medical Genetics. Lark and University of Utah research associate Kevin Chase used this same collection of Portuguese water dog X rays and pedigrees to identify the genes that control a major dog disease: hip dysplasia. This misalignment of the back leg’s ball joint in the pelvic bone’s socket leads to degenerative joint disease seen often in older dogs of large breeds from Labrador retrievers to shepherds to Newfoundlands. Veterinarians had previously noticed that left hips were affected more often than right hips, though many dogs suffer dysplasia in both hips. (Hip dysplasia is also found in approximately one in 100 humans, and the left hip is affected more often in us, as well.)
Lark and his team were surprised by what their comparison of genetics and skeletal structure showed: Two different groups of genes were independently controlling hip bone alignment on opposite sides of the body. “We found a locus [location of genes] that is preferentially acting on the left hip and one that acts on the right hip. They’re quite separate,” he says.
Separate control of right and left hips helps explain why the left is affected more frequently than the right. And using genetic screening to predict a certain dog’s tendency toward hip dysplasia while it’s still of breeding age—instead of waiting for the disorder to manifest as the animal gets older—will be of great value to breeders whose reputations and livelihoods depend on breeding the healthiest, longest-lived dogs. “This finding is of real interest, unexpected and quite exciting,” Lark says.
Not only are the results from Lark’s work exciting, but his methods also require an unusually low level of involvement by research subjects and their owners. Scientists benefit because they don’t pay a dime for the upkeep of their research subjects. And the Portuguese water dogs live happy lives in loving homes while their X rays and blood samples are under intense scientific scrutiny.
Lark says this aspect of the project is worthy of attention from bioethicists because people care for their dogs like they care for their children. “Using the dog as a model system for the ethics of genetic research and of genetic problems may be one of the best systems [researchers] can use, because almost every reaction they get will be based on human emotion, human reaction, which is exactly the basis for all our ethics,” he says. “And dogs are just perfect for that.”
—Lena DeTar is a Utah native who briefly attended the University
of Utah. She recently completed a master’s degree in science writing
at Johns Hopkins University.
For the benefit of present and future dog owners involved in this project, Lark and colleagues have created a Web site detailing in lay terms their methods, the scope of their testing and an overview of population genetics. This and more information about the lab may be found at www.georgieproject.com.
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