Excessive handwashing, counting, throat clearing or blinking. These behaviors, sometimes diagnosed as symptoms of obsessive-compulsive disorder (OCD) in humans, can also be found in dogs and other animals. Of course, a dog can’t wash its hands repetitively — but it might lick its paw over and over, or suck on its flank until it's raw.
For 20 years, veterinary behaviorist Nicholas Dodman and neurologist Edward Ginns have worked to prove there’s a link between repetitive dog behaviors and compulsive human ones. They’ve since found the genetic pathways that drive the severity of canine compulsive disorder and believe their research on dogs will help humans suffering from OCD too.
According to the National Institute of Mental Health, OCD afflicts more than 2 million adults in the U.S., or an estimated 1.2 percent. And the World Health Organization lists OCD as one of the 20 most disabling diseases for humans. Despite this, there’s currently no cure for the disorder and therapies — including cognitive behavioral therapy and medication — benefit only about half of the patients who seek help.
In the Genes
Dodman and Ginns’ research, published in the International Journal of Applied Research in Veterinary Medicine in 2016, is based on a decade of studying purebred Doberman Pinschers. They determined that “four genes — CDH2, a neural cadherin, and three serotonin genes — modify severity [of OCD],” says Dodman, a professor emeritus of Tufts University’s Cummings School of Veterinary Medicine. Further, they found that structural brain abnormalities in the dogs with canine compulsive disorder (CCD) were similar to humans with OCD.
This year, researchers in China replicated their findings. Using different compulsions and a different breed, Dodman says the investigators “confirmed the involvement of the CDH2 gene” in the Belgian Malinois, which repetitively runs in a geometric pattern. But for Dodman, the icing on the cake was when a group of researchers in South Africa “looked for the CDH2 gene in human OCD and found that it was implicated.”
Dodman and Ginns believe that continued research on CCD is the path to finding a cure for human OCD. That’s because dogs come by their affliction naturally (unlike lab animals, which are inflicted with diseases in the interest of research). And their lack of genetic diversity within breeds allows a small study group of 100 bull terriers, for example, to result in meaningful data, says Dodman. Similar studies on humans would require 10 to 20 thousand people and cost millions of dollars, he adds.
Nature vs. Nurture
But they don’t believe OCD can be explained only by genetics. According to Ginns, who is a professor of psychiatry at the University of Massachusetts Medical School, OCD is a complex trait that is clearly identified as both genetically and environmentally influenced. Stress, specifically, “can affect cognitive and other brain function. And we’re just beginning to really appreciate that impact,” he says.
For one, OCD isn’t found in all human populations; the natives of New Guinea, for example, "don't have anxiety-driven compulsive disorders and fears about personal safety other than the real ones that they're actually living with,” Dodman says. It is, however, found in millions of people in the “concrete jungle,” he adds, where there’s artificial lights flickering, computer screens, lack of exercise and lots of television.
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Similarly, OCD isn’t found in the wild but is rampant in zoos — from giraffes and elephants “weaving,” or bobbing their heads from side to side, to sea lions and polar bears “cycling through the water,” Dodman says. “The anxiety comes from stemming their natural species’ typical behaviors.” In other words, their survival mechanisms have gone awry.
Outside of zoos, horses, which spend 60 to 70 percent of their time in the wild grazing, will exhibit mouth-related compulsions when they can’t roam free. “[They] chew on things, because they're not fed in a natural way. They're not grazing all day long. They get their food in the bag twice a day,” Dodman says. “And they can't walk anywhere because they're in a 12- by 15-[foot] stall.” Instead, they walk around in circles, also known as stall walking.
Every Dog Has Its Day
“When squeezed, [these behaviors] pop out of the Pandora's box into these now psychiatrically defined conditions. So every species does exactly what you'd expect it to do,” Dodman says.
Dog compulsions run along breed lines. “These small groups, called breeds, are really useful for finding the genetics, the pathways, to provide new treatments for people,” Dodman says. Dogs with long coats may demonstrate compulsive licking because they must look after their coats in real life, he adds. Similarly, bull terriers are chasers — they tend to run in circles, chase things and develop an obsession with objects.
It’s taken decades of research for the two researchers to convince the world that dogs and other animals suffer a form of OCD too. “When we first started talking about OCD and animals, there were disbelievers,” Dodman says. But now, even those who had the biggest doubts are changing their minds. Dodman now heard from colleagues who admitted to him that they are “beginning to understand this animal OCD thing … It only took 20 years.”