Genes could explain why women are more prone to stress-related anxiety and mood disorders.
Women seem to react worse to negative experiences
US researchers have pinpointed a variation in a gene which controls regulation of a key brain chemical linked to mood.
Their work, on monkeys, suggests people with this variant may be more likely to react badly to negative experiences.
The US National Institute on Alcohol Abuse study appears in Proceedings of the National Academy of Sciences.
The researchers focused on a particular variant of the gene, known as the s allele.
People with this variant produce less of a protein that is involved in regulating levels of a chemical called serotonin in the brain.
Previous research has suggested that people were more likely to become depressed after going through a bad experience if they carried this gene variant.
For the latest study, the researchers measured stress hormone levels in 190 infant rhesus macaque monkeys when the animals were the equivalent of about nine to 24 months old in human development terms.
Some of the measurements were made after the animals had been socially separated for 30 minutes - a situation which causes stress among monkeys which are used to each other's company.
The scientists found that, after social separation, the highest levels of stress hormones were found among female animals that both carried the s allele, and had a history of adversity.
They say that if their results can be applied to humans they suggest that females who carry the s allele may be particularly vulnerable to developing mood disorders after being exposed to stress early in life, such as childhood abuse or neglect.
Researcher Dr Christina Barr told BBC News Online it was unclear why men and women should react differently. However, she said it was possible that sex hormones also play a role.
The researchers hope their work will eventually help to predict, treat and ultimately prevent certain human neuropsychiatric disorders.
Iain Ryrie, assistant director of research at the Mental Health Foundation said the research was interesting, and underlined the need to consider the role of different factors, such as genetics and environment, in mental illness.
But he said it would be wrong "to over-stress the genetics of childhood adversity.
"They are an important but partial explanation. Were we to turn our attention to humans rather than monkeys, related research is available which draws different conclusions.
"For example, the level of stress related hormone found in the blood stream fluctuates according to our levels of exercise, diet and the quality of our human relations."
He added: "There is much we can do after our genes are laid down to enhance our ability to cope with stress and thus avoid some of its debilitating consequences.
"Over-stressing genetics risks missing this point and the opportunites it presents."