Revealed: The brain flaw 'that causes compulsive behaviour'

OCD, in which obsessive thoughts drive sufferers to carry out bizarre and repetitive rituals, affects up to 3 per cent of the population.

Symptoms may include repeated hand-washing, the constant need to check doors are locked and the arranging of items in a specific order.

But despite OCD affecting up to two million people in Britain, there is no failsafe test or treatment for the condition.

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Identifying brain regions involved in the disease, which is known to run in families, could be the first step in developing new drugs and diagnostic tests.

The Cambridge University researchers took brain scans of 31 people with OCD and of close Brain f law "that causes compulsive behaviour" family members.

A healthy group, with no family history of the condition, was also scanned. Comparison of the images revealed the OCD patients and their relatives had less grey matter in parts of the brain that control behaviour.

The difference was particularly striking in regions that control our ability to suppress thoughts and actions, the journal Brain reports. Researcher Lara Menzies said the findings showed that OCD was associated with patterns in brain structure which run in families.

She said: "Impaired brain structure in areas of the brain associated with stopping motor responses may contribute to the compulsive behaviours that are characteristic of OCD. These changes appear to run in families and may represent a genetic risk factor.

"The current diagnosis of OCD is subjective and so knowledge of the underlying causes may lead to better diagnosis and improved clinical treatments."

Diagnosis involves a check-list of symptoms and does not spot all cases. Treatment, including counselling and anti-depressants, does not work for everyone, and many suffer side-effects.

Possible contributory factors include traumatic childhood events and hormonal changes in pregnancy. Last year, David Beckham revealed he suffered from OCD, one of the top ten most debilitating illnesses according to the World Health Organisation.