Brain region linked to obsessive disorder risk

Brain activity was normal in volunteers without the disorder.

"If this part of the brain isn't acting as it should it predisposes you to OCD," Chamberlain said. "Previous studies had only shown this in patients, not the unaffected relatives."

The findings could help identify people at risk to provide treatment before symptoms emerge, and lead to a biological marker to determine who is at greatest risk, he added.

Current treatments include Prozac, drug that belongs to a class of compounds called selective serotonin reuptake inhibitors (SSRIs).

U.S. drugmaker Eli Lilly and Co introduced Prozac in 1987 but the medicine is now off patent and widely available generically as fluoxetine.

(Reporting by Michael Kahn; Editing by Maggie Fox and Jon Boyle)