AR-News: Undoing doggy damage: Intensive breeding has produced many defects

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Undoing doggy damage
Intensive breeding has produced many defects, and genetics may hold the keys to eliminating them

   
BY EARL LANE
WASHINGTON BUREAU

March 25, 2004


WASHINGTON -- Dogs are the most variable group of mammals on the planet, experts say, thanks to the intervention of humans.

We have lived with them for thousands of years and have bred them intensively in recent centuries for desirable traits.

Even as that breeding has produced tremendous diversity, from the Chihuahua to the St. Bernard, and such special skills as herding, hunting and guarding, it also has led to a host of inbred genetic disorders that affect the more than 300 known breeds.

There are hopeful developments. During the past decade, about two dozen diagnostic tests have become available for certain genetic disorders in dogs. The tests can help breeders avoid perpetuating some of the common ailments in dogs.

Such efforts, which have had mixed success, are about to receive a powerful boost with the completion of an ambitious project to sequence the genome -- the genetic blueprint -- of the dog in great detail.

That effort should help lay the groundwork for more rapid discovery of disease genes in dogs and development of additional screening tests, specialists say. A better understanding of the dog genome also is expected to provide more insight into the genetic origin of diseases that purebred dogs share with humans, including cancer, epilepsy, heart disease and several eye disorders.

Nearly 400 genetic defects and diseases have been described in dogs, according to Norine Noonan, dean of sciences and mathematics at the College of Charleston in South Carolina and a basset hound breeder.

There are estimates that one dog in every 400 has a genetic disorder. Some breeds have a high incidence of problems. There are about 140 genetic disorders affecting the German shepherd breed, according to Noonan, ranging from subtle flaws in a dog's physical appearance to severe hip problems. Among Doberman pinschers, 77 percent have the gene for von Willebrand's disease, a bleeding disorder similar to hemophilia.

Much to learn

"We've used dogs as our evolutionary lab," Noonan said in a recent interview. "We have exerted a tremendous amount of selection pressure, based on a human notion of what we wanted those breeds to accomplish."

Nor are the problems limited to purebred dogs. Noonan said more than 200 genetic problems have been identified in mixed-breed mongrels.

Because of the genetic history of dogs and their kinship with humans, researchers are paying increasing attention to doggy DNA. A team of scientists announced last year they had used a rapid new method to sequence nearly 80 percent of the genome of a standard poodle. In that rough draft of the dog's genetic blueprint, the team found an equivalent dog gene for 75 percent of known human genes.

A key study

Now, another team from the Broad Institute of Harvard and MIT in Cambridge, Mass., is completing a project that will have significantly better coverage of the entire genome of a female boxer named Tasha. The location of every chemical building block in the dog's DNA will be determined with a high degree of accuracy, according to specialists. That sequencing effort is expected to be completed by late spring or early summer.

"We're all looking forward to the canine genome project providing information that can be used by researchers in developing more tests" for dogs, said John Duffendack, president of VetGen, an Ann Arbor, Mich., company that offers canine genetic tests.

The new data should "greatly accelerate the research that is being done," agreed Jeanette Felix, president of OptiGen, a company in Ithaca that also offers genetic tests for dogs. She cautioned that some of the ailments of most interest to dog breeders and owners, including hip deterioration, eye cataracts and epilepsy, are likely caused by the interaction of multiple genes, making a diagnostic test difficult.

A tool for breeders

Still, Noonan said the completion of the dog genome "may open the vistas for unprecedented progress in canine health."

Even if new tests do become available, however, they will be of use primarily to breeders rather than individual dog owners, Felix said. "The only reason the average dog owner might become interested," she said, "is if there was a cost-beneficial therapy or treatment for a disease" whose gene is identified.

Her company offers tests in more than a dozen breeds affected by forms of progressive retinal atrophy, an eye disorder that can lead to blindness. There is no treatment now available to reverse the disease, she said. The screening tests, ranging in cost from $120 to $260, can determine whether a dog is a carrier of the genetic trait. Breeders can then refrain from mating the dog with another carrier, which can produce offspring with the disease.

No guarantees

In theory, genetic tests will enable breeders to eventually eliminate the disease from a breed with selective mating. In practice, the process is expected to be a slow one since there are no laws or rules mandating that available tests be used for affected breeds. Ultimately, it depends on the amount of interest shown by breeders, specialists said, and that can vary.

The Irish Setter Club of America funded research to develop a test for progressive retinal atrophy in setters. The club requires breeders to make every effort to learn about inheritable traits of their dogs.

"We don't have a mandatory testing program, but our peer pressure has worked very well," said Connie Vannacore, a New Jersey-based breeder of Irish setters who chairs the club's health committee. "Most of the breeders will test." 
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