Canadian researchers, reporting online today in Nature Neuroscience, looked at the combined effect of childhood abuse and a stress hormone-related gene on the hippocampus, the part of the brain involved in memory and learning.

They studied the brains of 12 suicide victims with a history of childhood abuse. They compared them with suicide victims with no history of child abuse and a control group who died of other causes.

They found significant differences in stress-related hormone receptors in those who had committed suicide and had been abused, compared with the others.

They also found evidence parts of the stress gene had been ''switched off'', resulting in an abnormal stress response in adulthood.

The executive director of the Institute of Health and Biomedical Innovation at Queensland University of Technology, Professor Ross Young, said childhood abuse appeared to interact with a stress hormone-related gene as one potential path to suicide.

''It reinforces the fundamental importance of the development of effective public policy and interventions to prevent child abuse so that this combined environmental and genetic risk can be dealt with,'' Professor Young said.

''We also need to ensure that we have effective interventions that assist adults who have been abused in childhood to respond effectively to stress.''

The study showed how the reduced expression of the gene led to an increase in hypothalamic-pituitary-adrenal response to stressful situations.

Such heightened hypothalamic-pituitary-adrenal responses have previously been linked to an increased risk of suicide, mood disorders and schizophrenia.

Early childhood experience has been shown to cause long-term genetic changes in the stress response pathway in rats, but this is the first evidence that the same thing happens in humans.

Professor Young said the research also underscored how ''being raised in a stable and safe environment as a child helps us deal with stress in adulthood''.

The director of the Australian Centre for Child Protection at the University of South Australia, Professor Dorothy Scott, said the study reinforced the importance of reducing children's exposure to abuse and neglect.

''It means that we must pay close attention to preventing and treating maternal mood disorders, both for the sake of the mother and her child,'' she said. with AAP