A new study conducted by researchers of McGill University in Montreal, Canada, has shown that childhood abuse victims can carry chemical changes to their DNA into adulthood.
Study leader Michael Meaney, a neurobiologist at the university, says that the research team observed that suicide victims with childhood abuse history were more likely to carry such chemical changes in their DNA as could affect their ability to respond to stress as adults.
He revealed that people without childhood abuse history did not show the same pattern of DNA modification, and had normal expression of NR3C1, a gene linked to stress responses.
However, Joan Kaufman, a psychologist at Yale School of Medicine in New Haven, Connecticut, who was not involved in the new study, said that the findings should not be taken to suggest that the effect of childhood abuse is indelible.
"The long-term effects of early abuse are not inevitable, and the more you understand about the mechanisms of risk, the more you can devise treatments," Nature magazine quoted her as saying.
The current research builds on animal studies that showed that rat pups that are stressed because they were raised by negligent mothers have extra methyl groups in their DNA in a region of the genome that controls expression of Nr3c1, the equivalent gene in rats.
The researchers point out that such 'methylation' can reduce gene expression.
NR3C1 encodes a protein expressed in neurons that responds to hormones called glucocorticoids. Lower expression of NR3C1 could be harmful because reduced responses to these glucocorticoids have been linked to increased stress.
With a view to seeing whether or not the results of animal studies translated into humans, Meaney and his colleagues collected brain samples from the Quebec Suicide Brain Bank.
They looked at samples from 12 suicide victims with a history of childhood abuse, 12 suicide victims with no history of childhood abuse, and 12 controls who had died suddenly from other causes.
The researchers revealed that people with a history of childhood abuse had lower levels of glucocorticoid receptors than those who had not been abused or had not committed suicide.
According to them, childhood-abuse victims had a similar methylation pattern to that seen in rats that had been stressed as pups.
Meaney, however, added that since his team have not yet looked for effects on egg or sperm DNA, it was doubtful that the changes could affect the germline.
The researcher also said that it was yet to be determined whether trauma as an adult produces the same pattern of changes.
Martin Teicher, director of the Developmental Biopsychiatry Research Program at Harvard Medical School in Belmont, Massachusetts, says that there may be times during childhood when the developing brain is particularly responsive to abuse.
His team imaged the brains of women who had been victims of child abuse, and found that those abused between the ages of three and five, or eleven and thirteen, had a smaller hippocampus - a region in the brain that is important for memory and learning - than those who had not been abused2.
With an eye on searching a way out, the researchers carried out studies on mice, and fould that the methylation changes could be reversed: if pups reared by negligent mothers are later treated with a chemical that removes DNA methylation, their stress responses return to normal.
However, presently, such drugs are not ready for use in humans, and could carry unwanted side effects.
But medication may not be the only way to treat victims of child abuse, for psychotherapy has been shown to produce chemical changes in the brain, and might be able to reset the methylation pattern, says Meaney.
"A social event got you into it. Could a social event get you back out? That's a very viable hypothesis," he said.
A research article on these findings has been published in the journal Nature Neuroscience.