Studies on brain signals in mice have lead to the discovery of a gene- Sapap3 - which may be linked to obsessive compulsive disorder (OCD) in humans, according to a study published in the journal Nature last week. Researchers at Duke University Medical Centre in North Carolina, reported that Sapap3 deficient mice exhibited OCD-like behaviour; showing signs of anxiety and compulsively grooming themselves, often to the point of injury.
Guoping Feng, Assistant Professor of Neurobiology at Duke and co- author of the study, said: 'We obviously cannot talk to mice to find out what they are thinking, but these mutant mice clearly did things that looked like OCD'.
Two per cent of the world's population are affected by OCD, which causes unwanted obsessive thoughts and repetitive behaviour, such as washing hands, checking or cleaning. The standard OCD treatment - Prozac - is only effective in about half of patients, highlighting the need for new treatments based on novel drug targets.
The researchers discovered the gene unexpectedly whilst studying an area of the brain known as the striatum, which acts as a 'relay centre'; receiving instructions from the cortex and shuttling them out to movement-related brain areas. Hidden cameras revealed that mice genetically engineered to lack the Sapap3 gene began to self-harm in adulthood and anxiously hid away in their cages.
To cancel out the possibility that the explanation was merely a skin irritation, the researchers administered the drug Prozac, to reveal that it cured the OCD-like behaviour in Sapap3 deficient mice. Switching the gene back on in mutant mice also had a curative effect, indicating that the missing gene was the cause.
In an accompanying editorial Steven Hyman, Professor of Neurobiology at Harvard Medical School, acknowledges that since the genetic and environmental factors contributing to psychiatric disorders are complex, the mouse model is far from perfect. 'The anxiety-like behaviours observed in these mice may also resemble OCD, but this requires a stretch of the imagination', he writes.
The next step will be to look for a human link between OCD and the human version of the Sapap3 gene by studying individuals who have a family history of OCD.