Dog genes could give OCD clue

Researchers in the US studying dogs have found a gene that is linked to the canine version of obsessive compulsive disorder (OCD). It is hoped that the findings will shed new light on the human condition, which is a complex disorder, difficult to study in man.

Dogs often exhibit characteristics reminiscent of the human OCD through actions such as tail-chasing, pacing and circling, and also harmful activities like licking their legs until they develop infections. These are continuations of normal predatory, grooming or locomotive behaviours, but parallel with human actions like hand washing, cleaning and checking objects that become repetitive in OCD.

A collaborative group of US researchers based at Tufts University, the University of Massachusetts Medical School, and the Broad Institute, studied the Doberman breed of dog, in which symptoms of canine compulsive disorder (CCD), manifested in the dogs sucking their flanks, are common and easily distinguishable. They took 92 dogs that exhibited symptoms of CCD and 68 dogs that did not, and compared their genomes using a genome-wide association study approach. They found that a variation in a gene called Cadherin 2 was more common in the affected dogs; in fact, dogs with this variation were two and a half times more likely to be affected by the disorder. The cadherin family of genes play important roles in embryonic development, making their function difficult to study in adults, but it is known that this particular cadherin is important in synapses in the brain. However, the researchers acknowledge that there is still much work to be done to investigate exactly how this gene influences normal behaviours in developing CCD in dogs.

Dr Nicholas H Dodman, veterinarian and professor of clinical sciences at the Cummings School of Veterinary Medicine at Tufts, was lead author on the paper, published in Nature Molecular Psychiatry. He says that the finding is likely to lead to a blood test that will help determine if dogs have the gene linked to CCD: 'If you don't want this problem, you can choose not to breed that particular dog', he explained. CCD is a hindrance for the normal activity for a dog, but can also result in bodily harm.

Dogs are more inbred and less genetically diverse than humans due to careful breeding, and also naturally develop diseases similar to humans, such as compulsive disorder, epilepsy, cancer and phobias. This makes them valuable tools for studying human disorders, as genes for complex disorders in dogs would be easier to find than in humans. Dr Dennis L Murphy, chief of the Laboratory of Clinical Science at the National Institute of Mental Health, US, was not involved with the study but is familiar with it and says: 'the research (into dogs) is helping us unravel the causes of certain kinds of diseases, including OCD, bipolar disorder and autism in humans'.

Dodman intends to study the bull terrier in the next tests, and other breeds will be the focus of future testing and research. Murphy is following the research by studying the same gene in humans, with samples from over 300 patients with OCD, 400 of their relatives, and about 600 people without OCD. He said: 'identifying a specific gene that could be a candidate gene for a complex disorder like OCD is a gift to have. This might be a quick route to a meaningful gene that just could be involved in the human disorder as well'.