DNA assessment identifies NME risk in pugs

DAVIS, CALIF. — A new DNA test created by the University of California, Davis, Veterinary Genetics Laboratory helps measure the risk of pug dogs developing necrotizing meningoencephalitis (NME).

According to Niels Pedersen, DVM, who has researched the disease and developed the latest test, it will allow breeders to select sires and dams that will produce puppies that are at significantly reduced risk of developing NME during their lifetime.

Puppies carrying the NME risk factor are nearly 13 times more likely to develop the disease. Prior to the test, about 2 percent of pug dogs died of NME.

"It is our hope that this mortality will be reduced to a small fraction of this percentage by selective breeding and with no loss of genetic diversity within the breed," Pedersen says.

But the test has limitations. According to Pedersen, it should not be used to diagnose NME or "to make a definitive judgment on the fate of any dog carrying the high-risk genotype."

Cecilia Penedo, PhD, UC-Davis associate director of Service and Genomic Research and Development at the Veterinary Genetics Laboratory, agrees that it is critical to understand that this is not a diagnostic test or tool for NME.

"It's not something veterinarians could use to determine whether a particular pug dog has the disease or not," she says. "It's mostly a breeding tool. Veterinarians who work with pug dog breeders might use the test as a recommendation to owners to know genetic composition of their breeding dogs. Veterinarians can use it more in terms of advising rather than diagnosing."

Only approximately one in seven dogs with the high-risk genotype will ever develop NME, according to Pedersen. Other triggers can contribute to disease development. For example, females are almost three times more likely to develop the disease than males, Pedersen notes.

Although the test accurately predicts the chances of a dog developing NME, a very small proportion of dogs with the non-susceptible genotype will also develop NME. It's very important that breeders understand this concept, Pedersen says.

The current test is what is called a "linked-marker test," explains Pedersen. "It tests for the presence of a small region of the genome that contains the ultimate gene or genes responsible for NME susceptibility. Such a test is made possible because the causative gene or genes is strongly linked to a much larger region on what is known as chromosome 12, which contains many of the genes that control the immune response," he says.

"The significance of this current test is that we can identify a DNA type that is associated with increased risk for the necrotizing encephalitis in pugs," Penedo adds.

The goal, according to Pedersen, would be to one day identify the actual causative gene or genes within this region and the specific gene defect(s) that predispose pug dogs to develop NME. Such a test may be more sensitive in detecting dogs at risk for NME.

The research was supported in part by a grant from the Canine Health Foundation of the AKC, as well as the UC-Davis Center for Companion Animal Health and Veterinary Genetics Laboratory.

Visit www.vgl.ucdavis.edu/services/PDE.php for more background on pug dog encephalitis.