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Preventing Canine Blindness Through Genetics

(reprinted with the permission of Morris Animal Foundation Animal News 4.1)

When man's best friend goes blind, it's stressful for the dog and the owner. Sadly, canine blindness isn't uncommon. One of its causes, progressive retinal atrophy (PRA), affects nearly every breed, says Dr. Gustavo Aguirre, a professor at Cornell University who will soon move to the University of Pennsylvania.

PRA is a group of inherited diseases that damage the cells that capture light in the dog's retina. As a result, the affected dog slowly goes blind. Because the disease is genetic, it is passed on by the parents. In some cases, both parents must carry the defective gene, while in other cases, one affected parent can pass on the trait. The disease is difficult to control through breeding because clinical signs of PRA usually don't emerge until later in life, after the dog has already passed on the bad gene. For this reason, the prevalence of PRA is on the rise. To stop its spread, Dr. Aguirre and his collaborator, Dr. Greg Acland, have already developed some tests that identify which dogs carry the PRA gene. The team continues to develop tests to help identify new forms of PRA so breeders can eliminate inheritance of the gene by choosing breeding pairs accordingly.

Morris Animal Foundation issued Dr. Aguirre his first grant to study PRA in 1993. At that time little was known about the disease.

"It's been a long effort because we had to develop all the tools needed to do this," Dr. Aguirre says. "The support from Morris Animal Foundation was critical for our work and ensured its rapid progress."

The first step was to develop a gene map, which was completed in 1997. The map allowed the investigators to determine where one type of PRA, progressive rod-cone degeneration (prcd), is located in the dog genome. They used that information to develop a DNA test to determine whether a dog carries the PRA gene. This study led investigators to the gene that causes dominant PRA in English mastiffs and bullmastiffs, day blindness in Alaskan malamutes and German shorthaired pointers, and X-linked PRA in Siberian huskies and Samoyeds. The test is being used to eradicate the disease in these breeds.

In addition, scientists can now use the tools developed by Drs. Aguirre and Acland to study other diseases, such as heart disease, kidney disease and hip dysplasia.

"The whole canine genetics community has benefited from our work," says Dr. Aguirre.

More work is needed, however. While the current test has greatly improved the diagnosis of PRA, it doesn't apply to all breeds. Rather, it must be applied on a breed-by-breed basis. Dr. Aguirre says more work is needed to determine the exact location of the gene that causes prcd, the most widespread form of PRA. This form of PRA affects many breeds, including Labrador retrievers, Portuguese water dogs, English and American cocker spaniels, Chesapeake Bay retrievers, Australian cattle dogs, poodles, Nova Scotia duck tolling retrievers and others.

Through a current Foundation-funded study, the investigators continue to analyze the gene map for additional information. If they can further pinpoint the gene that causes prcd, they will be able to develop a more specific test that could lead to gene therapy techniques and, someday, the ability to eradicate all forms of the disease in all breeds of dogs. For more information on blindness, please contact your veterinarian.

Co-sponsors: Hal & Marty Hendershot; James R. & Mary Ann Meyer; National Entlebucher Mountain Dog Association(NEMDA);The Seeing Eye, Inc.

To learn more about other canine health studies, please visit our Web site at www.MorrisAnimalFoundation.org.