A gene variation that was thought to work with a stressful life to produce depression may not have much of effect, according to a new research.

"Rigorous re-evaluations of published studies provide the checks and balances necessary for scientific progress," said Dr. Thomas R. Insel of the National Institute of Mental Health. "We are still in the early days of understanding how genes and environment interact to increase the risk for depression."

In 2003, researchers said that a gene involved in serotonin activity in the brain increased the risk of major depression in people who had a number of stressful life events over a five-year period.

But the new study found that efforts to reproduce that result have been inconsistent, according to a media release on the new evaluation, which looked at more than 14,000 patients in 14 different studies.

The researchers said that the problem came from trying to tie genetic problems to events in people's lives, which makes it harder to tease out the actual effect of the gene.