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Genetic discoveries fuel veterinary medicine

By cracking open the textbooks of life through the sequencing of the canine and feline genomes, researchers are discovering new approaches to pet health and disease.
Denali, a Maine Coon cat, gets a ride back to his cage at the CFA-IAMS Cat Championship in New York
Denali, a Maine Coon cat, gets a ride back to his cage at the CFA-IAMS Cat Championship in New York on Oct. 8. The cracking of the feline genome has allowed researchers to identify a gene in Maine Coon cats that causes a common form of heart disease.Seth Wenig / Reuters file

Ricky, a Devon Rex cat, played the piano, jumped through a hoop, and was once mistaken by a bank teller for a wind-up toy. Ricky had another, less-fortunate distinction: he suffered from hypertrophic cardiomyopathy, the most common form of heart disease in cats.

When Ricky died of a massive heart attack in 2002, his owner, Steve Dale of Chicago, set up The Ricky Fund for research into feline hypertrophic cardiomyopathy (HCM) in conjunction with the Winn Feline Foundation, which funds research into cat-related health problems. Since then, among the advances researchers have made include identification of the gene that causes HCM in Maine Coon cats, a great step in the path toward treating the disease.

By cracking open the textbooks of life through the sequencing of the canine and feline genomes, researchers are discovering new approaches to pet health and disease. They’ve begun to identify the genes responsible for certain inherited diseases and create genetic tests to identify affected animals. These breakthroughs mean new hope for people whose cats and dogs suffer from such diseases, as well as for breeders, who can use new techniques to screen for disease and prevent passing it on.

“Finding the gene [for HCM] will lead to the availability of a genetic test to identify affected Maine Coon cats in the near future, and it will spur research to see if the same gene is responsible for the disease in other types of cats," says Susan Little, a veterinarian in Ottawa, Ontario, Canada and president of the Winn Feline Foundation. “Finding the gene responsible for a disease always opens the potential that new treatments will be found as well.”

Winn-funded researchers have also identified the gene responsible for polycystic kidney disease (PKD), which affects 30 to 40 percent of Persian cats and related breeds, such as Himalayans.

“With the identification of the PKD gene has come a simple genetic test to identify affected cats, and hopefully it will lead to a treatment for cats that develop chronic renal insufficiency due to their PKD,” Little says.

Early screening
With this test, breeders can screen kittens as young as 8 weeks of age for the PKD gene and replace any PKD-positive cats in their breeding program over time. Because the gene is found in such a large proportion of Persians and related breeds, it’s important for breeders to eliminate the gene slowly so as not to restrict genetic variability.

“Restricting genetic variability would lead to more health problems,” Little says. “Eventually, there should be very few Persians born with PKD, something that will bring peace of mind to pet owners. Pet owners who have Persians now can also get them screened for the gene and learn more about the disease.”

Some diseases are genetically complex, linked to more than one gene. In the past, that’s been a difficult issue for breeders and researchers, especially if diseases don’t occur until later in life. By the time the disease shows up, the animal may have offspring that also carry the genes for the disease.

“New genetic tests should really help us deal with issues like that,” says veterinarian Patricia Olson, president and CEO of Morris Animal Foundation in Englewood, Colo. “We should have some very good tools that can tell us earlier if an animal is predisposed to something. It doesn’t mean you don’t utilize that animal in breeding, but you utilize it in a way that the carrier is mated appropriately and doesn’t pass on the disease. You want to optimize the good traits, not pass on the bad, and have the tools to be able to make the difference.”

New vaccines in the works
Another breakthrough is in the area of vaccines for cats. Vaccine sarcomas — cancer that forms at the injection site of a vaccination — are uncommon in cats, but a higher-than-normal incidence of them, which was first noticed in 1991, caused veterinarians to take a second look at the possible causes.

“No one has been able to prove an absolutely spot-on, definitive link between vaccine A and tumor B, but it’s fairly well accepted that the suspects were rabies and feline leukemia vaccine,” says Robin Downing, a veterinarian in Windsor, Colo., president of the International Veterinary Academy of Pain Management.

The adjuvant — the compound added to vaccines to stimulate the immune system — is the most likely culprit, although again no one has proven a definitive link, Downing says.

“There’s enough of an implication that many of us were nervous about a linkage between the adjuvant and the tumors," she says. "So now we have a series of vaccines available to us that use recombinant DNA science to avoid the need for an immune stimulant or that are delivered in new ways. For cats, we have a distemper vaccine that is delivered using a few drops on the nasal mucous membrane. For leukemia virus, we not only have recombinant DNA vaccines but also air-driven delivery into the skin. The rabies vaccine is still an injectable vaccine; however, it’s recombinant DNA technology.” Vaccines using recombinant DNA technology are also available for dogs.

Hope for better cancer care
Cancer is a major concern as well. “By being able to evaluate the genetic contribution to these diseases, as well as environmental and nutritional triggers, we can look at animals in a really different way,” Olson says. “When you look at cancer, for example, you’ve got golden retrievers who are at risk for one type of cancer and Boston terriers for another, and if you can start to tease out [the different genes responsible], it could be extremely powerful.”

Veterinary cancer researchers are actively working to target certain cancers with gene therapy, in particular melanoma. Their goal is to manipulate the genes of mutated cells to help the body’s immune system fight the cancer.

Genetic-based treatments may not be that far in the future.

“Now that the canine genome has been mapped, I can’t wait for the next wave of information that will come from that,” Downing says. “I won’t be surprised if within a five-year period I can target some diseases genetically, whether they’re cancer or congenital problems. I’m not sure I necessarily would be willing to expect it, but I won’t be surprised.”

Kim Campbell Thornton is an award-winning author who has written many articles and more than a dozen books about dogs and cats. She belongs to the Dog Writers Association of America and is past president of the Cat Writers Association. She shares her home in California with three Cavalier King Charles Spaniels and one African ringneck parakeet.