Abuse in early childhood permanently alters how the brain reacts to stress, a Canadian study suggests.
Analysis of brain tissue from adults who had committed suicide found key genetic changes in those who had suffered abuse as a child.
It affects the production of a receptor known to be involved in stress responses, the researchers said.
The Nature Neuroscience study underpins the impact of stress on early brain development, experts said.
Previous research has shown that abuse in childhood is associated with an increased reaction to stressful circumstances.
But exactly how environmental factors interact with genes and contribute to depression or other mental disorders in adulthood is not well understood.
A research team led by McGill University, in Montreal, examined the gene for the glucocorticoid receptor - which helps control the response to stress - in a specific brain region of 12 suicide victims with a history of child abuse and 12 suicide victims who did not suffer abuse when younger.
They found chemical changes which reduced the activity of the gene in those who suffered child abuse.
And they showed this reduced activity leads to fewer glucocorticoid receptors.
Those affected would have had an abnormally heightened response to stress, the researchers said.
It suggests that experience in childhood when the brain is developing, can have a long-term impact on how someone responds to stressful situations.
But study leader Professor Michael Meaney said they believe these biochemical effects could also occur later in life.
"If you're a public health individual or a child psychologist you could say this shows you nothing you didn't already know.
"But until you show the biological process, many people in government and policy-makers are reluctant to believe it's real.
"Beyond that, you could ask whether a drug could reverse these effects and that's a possibility."
Dr Jonathan Mill, from the Institute of Psychiatry at Kings College London said the research added to growing evidence that environmental factors can alter the expression of genes - a process known as epigenetics.
"Whilst these results obviously need to be replicated, they provide a mechanism by which experiences early in life can have an effect on behaviour later in adulthood.
"The exciting thing about epigenetic alterations is that they are potentially reversible, and thus perhaps a future target for therapeutic intervention."