The Leonberger dog breed is named after the city of Leonberg, Germany, and was bred to resemble the lion on the city’s coat of arms beginning in the mid-1800s. They are one of the largest dog breeds on Earth. It’s not uncommon for a male to weigh up to 170 pounds, a fact that pushed the breed to near-extinction during World War II.

“It was almost impossible to care for a dog that big during wartime,” says Katie Minor, lab manager of the College of Veterinary Medicine’s (CVM) Canine Genetics Lab, and in 1946, there were only 17 dogs registered in the breed.

The breed numbers have slowly grown. While still a relatively rare breed, there are some 30,000 Leonbergers in the world today, all of whom can trace their lineage back to the small group that survived World War II. Because the breed was revived from so few individuals, its gene pool is shallow, which can lead to hereditary health conditions.

With ongoing support from the Leonberger Health Foundation, the University of Minnesota’s (UMN) Canine Genetics Lab, together with the University of Bern, Switzerland, has spent two decades identifying the genes that cause common disorders in Leonbergers, from three forms of polyneuropathy—a disease that damages nerves, causing weakness, difficulty walking, and severe difficulty breathing—to a rare central nervous system disorder that affects the brain and spinal cord.

The community of Leonberger breeders was already extremely dedicated to banking their dogs’ genes, understanding how important this was for a breed that nearly went extinct. That has created a unique opportunity to study genetic conditions in Leonbergers. The UMN Canine Genetics Lab and the University of Bern together house DNA samples from more than 11,000 Leonbergers.

“We pretty much get DNA samples from every breeding dog, and it’s an incredible resource for studying breed health,” Minor says.

Research with a real-world impact

In 1999, G. Diane Shelton, a pathologist at the University of California, San Diego, found a small but noticeable pattern of laryngeal paralysis and polyneuropathy in Leonbergers. Back then, the team thought it was a rare genetic condition inherited through a gene on the X chromosome. If this were the case, it would be easy to breed the condition out of the lineage.

Armed with that information, the Canine Genetics Lab got to work looking for the gene, which turned out not to be X-linked at all. Over the next two decades, researchers at the Canine Genetics lab have worked closely with their colleagues at the University of Bern and the Leonberger Health Foundation to identify three genes that cause neuropathy disease in Leonbergers, as well as a gene that causes a central nervous system disorder called leukoencephalomyelopathy. The teams have also discovered that these genetic variants are significant for other breeds as well.

“Leonbergers are closely related to St. Bernards, and both have at least two of the same gene mutations that cause disease,” Minor says. “The most common neuropathy gene we found is also in American Staffordshire terriers, English bulldogs, golden retrievers, great danes, Labradors, and others, so the discovery in Leonbergers is helping breeds we didn't even know had these mutations.”

The Leonberger Health Foundation provides much more than financial support for the project. Minor works closely with teams at the foundation to develop health surveys, in which breeders and owners can report any new conditions they are seeing pop up in the breed. Over the past several years, the foundation reported an uptick in the number of cataract cases and issues with infertility among Leonbergers—conditions that have become some of the Canine Genetics Lab’s next targets.

The effort is truly a collaboration between the foundation, multiple universities, and especially the breeders who have revived the Leonberger breed.

“The breeders are really good about testing their breeding dogs for the genetic mutations discovered through this work. They are careful not to pair two dogs together that carry mutations for recessive diseases. This has greatly reduced the number of dogs that are affected with these disorders,” says Eva Furrow, an associate professor of internal medicine and one of the principal investigators in the Canine Genetics Lab.