Genetic mutation in labs identified

WCVM researcher Dr. Sue Taylor examines Breeze, her Labrador retriever. Photo: Debra Marshall.

Researchers at the University of Saskatchewan’s Western College of Veterinary Medicine and the University of Minnesota’s College of Veterinary Medicine have identified a genetic mutation in Labrador retriever dogs that is highly associated with exercise-induced collapse (EIC) syndrome.

The findings published this week in Nature Genetics are expected to help dog breeders gradually reduce the number of Labradors with the trait in future generations.

After intense hunting or retrieving exercise, EIC-affected Labradors start to lose control of their hind limbs. In most cases, their legs get wobbly and their limbs give out. In rare cases, the dogs may die. Labradors are the most common dog breed in the world and an estimated three to five per cent of Labradors have this condition.

“After 13 years of working on this problem, we now have the definitive answer about the syndrome’s true cause for Labrador breeders and owners. This discovery will have a huge impact on the Labrador breed worldwide.” says Dr. Susan Taylor, a professor of small animal internal medicine at the WCVM.

“This is very exciting because it is the first naturally occurring mutation of this gene identified in any mammal,” adds James Mickelson, professor of veterinary sciences and a genetic researcher at the University of Minnesota. “Its discovery could offer insight into normal as well as abnormal neurobiology in both animals and humans.”

The research team identified a mutant form of the dynamin 1 gene as highly associated with EIC. The dynamin 1 protein normally maintains proper chemical communication between adjacent nerves, also known as synaptic transmission.

The mutated form of the dynamin protein in dogs with EIC appears to have diminished function. As a result, synaptic transmission is interrupted during intense exercise and excitement, causing collapse.

The researchers have also developed a genetic test for the mutated gene and determined that up to 30 per cent of Labrador retrievers are carriers of the mutation. EIC is inherited as an autosomal recessive trait, with affected dogs inheriting one copy of the mutation from each parent. Owners can have their dogs tested through their veterinarian by submitting a blood sample to the University of Minnesota Veterinary Diagnostic Laboratory.

Taylor and her WCVM colleague, small animal surgeon Cindy Shmon, initiated a comprehensive clinical investigation of EIC in 1995 after examining an affected dog that was referred to the WCVM Veterinary Teaching Hospital. Suspecting that the syndrome had a novel genetic basis, Taylor contacted Mickelson and Edward Patterson at the University of Minnesota in 2001.

“The genetic research was based on more than 300 blood samples and pedigrees that we collected from affected and unaffected Labradors throughout North America,” says Taylor, who breeds Labradors and competes with them in retriever field trials.

The EIC research received financial support from the Morris Animal Foundation, the American Kennel Club Canine Health Foundation and the WCVM’s Companion Animal Health Fund.