There may be a genetic explanation for why that guy next door washes his hands for hours, or repeatedly checks the lock on his front door. He is among the two per cent of the population that suffers from obsessive-compulsive disorder (OCD), a neuropsychiatric anxiety disorder which new research pinpoints to a genetic cause.
The support for a genetic explanation for OCD comes from researchers at U of T and their colleagues at the University of Michigan. In dual research papers published in July, the groups reported a link between OCD and a gene encoding a glutamate transporter in the brain called SLC1A1.
“We found that a variant of this gene is consistently transmitted to a person with OCD,” said Dr. Paul Arnold, a psychiatrist at Hospital for Sick Children and the lead investigator of the Toronto group.
Neurotransmitters, the molecules relaying information between brain cells, must pass through gateways, or transporters, which control the flow of molecules. A transporter of glutamate, a type of neurotransmitter, is encoded by the gene SLC1A1. Researchers decided to focus on this gene in OCD patients for two reasons. In a genome scan of OCD patients, the region of the genome most strongly associated with OCD was found to contain the SLC1A1 gene. The function of the glutamate neurotransmitter in the brain as correlating with OCD was another point of interest.
While these results are encouraging, Arnold cautioned that we don’t exactly know what the variant of this gene means-does it affect the function of the gene or is it a marker of something else?
“It’s possible we are just in the right general area of the gene,” explained Arnold. “For example, we know the problem is in Toronto, but we don’t know if it’s in North York or Scarborough.”
Until now, the serotonin system, another neurotransmitter, has been the focus of OCD research. While drugs that make use of the serotonin system help alleviate OCD symptoms, it’s possible the medication is inadvertently targeting another system, like the glutamate transporter system.
“Disorders like OCD are probably quite complex,” said Arnold. “It’s quite conceivable that genes in both the glutamate and serotonin systems could be involved in some kind of combination that we don’t really understand.”
Although the research points to a strong biological basis for OCD, the possibility of environmental influences can never be left out of the picture.
“Genes act within an environmental context,” said Arnold. “Take a gene for aggression, another behavioural trait that is thought to have a genetic component. If you are in a situation where aggression makes you survive…that’s a good thing with regards to enhancing your ability to pass on your genes. But if you are put in a situation where…being aggressive makes you stand out from a group and you may get punished for it, that’s not such a good thing anymore.”
