The brains of people who commit suicide are chemically different to those who die from other causes, a Canadian study has suggested.
Researchers analysed brain tissue from 20 dead people and, in those who killed themselves, they found a higher rate of a process that affects behaviour.
Writing in Biological Psychiatry, they said it appeared environmental factors played a part in the changes.
And they said the discovery opened up a new avenue of research.
This is exciting new evidence that genetic and environmental factors may interact to produce specific and long-lasting modifications in brain circuits
John Krystal, Biological Psychiatry editor
The researchers, from the University of Western Ontario, Carleton University and University of Ottawa, analysed tissue from 10 people who had a serious depressive disorder and had committed suicide and 10 who had died suddenly from other causes, such as a heart attack.
They found that the DNA in the suicide group was being chemically modified by a process normally involved in regulating cell development, called methylation.
It is methylation which shuts down the unwanted genes in a cell - so the necessary genes are expressed to make a cell a skin cell rather than, for example, a heart cell.
The rate of methylation in the suicide brains was almost 10 times that of the other group, and the gene that was being shut down was a chemical message receptor that plays a major role in regulating behaviour.
In the paper, the researchers suggest this reprogramming could contribute to the "protracted and recurrent nature of major depressive disorder".
Previous research has suggested that changes to the methylation process can be caused by a combination of genetic and environmental factors called epigenetics.
Modifications 'shape life'
Dr Michael Poulter, who led the research, said: "The whole idea that the genome is so malleable in the brain is surprising, because brain cells don't divide.
"You get dealt your neurons at the start of life, so the idea that there are still epigenetic mechanisms going on is pretty unusual."
He said the findings of the study opened up a new avenue of research and potential therapies for depression and suicidal tendencies.
John Krystal, the editor of Biological Psychiatry, said: "This is exciting new evidence that genetic and environmental factors may interact to produce specific and long-lasting modifications in brain circuits.
"Further, these modifications may shape the course of one's life in extremely important ways, including increasing the risk for major depressive disorder and perhaps suicide."