Children who are exposed to violence experience wear and tear to their DNA that is similar to that seen in aging, according to a new study that may help explain why they face a heightened risk of mental and physical disorders as adults.
In a long-term study of 118 pairs of identical twins, researchers at Duke University found that boys and girls who had experienced violence had shorter genetic structures called telomeres than youngsters who had more peaceful upbringings.
The children in the former group had been physically abused by an adult or bullied frequently, or had witnessed domestic violence between the ages of 5 and 10. And the more types of violence a child had experienced, the faster his or her telomeres eroded, said study leader Idan Shalev, who published the findings Tuesday in the journal Molecular Psychiatry.
Telomeres are strands of protective DNA that cap the tips of chromosomes inside the cell. Each time a cell divides, the telomeres get a little bit shorter. After about 50 to 60 cell divisions, the telomeres become so small that the cell begins to shut itself down.
Scientists have demonstrated a link between shortened telomeres and susceptibility to disease, suggesting that they are a useful gauge of biological age, Shalev said. Stress seems to speed up the telomere erosion process, he added.
Previous research had already established that people who had experienced childhood stress had shorter telomeres as adults. Shalev and his colleagues sought to find out whether the DNA damage occurred around the time that stressful events took place.
They turned to children from the British Environmental-Risk Study, which tracked 1,116 sets of same-sex twins born in 1994 and 1995. All of the children provided cells through cheek swabs when they were 5 and 10 years old, but because it was too costly to measure telomeres in all of the children, the Duke researchers focused on a subset of identical twins who lived near London, including many with teenage mothers.
The researchers measured telomeres in tens of thousands of cells from each child, ultimately establishing an average telomere length. Through interviews with primary caregivers, the team also assessed the subjects' exposure to violence at ages 5, 7 and 10.
Telomere length declined in all the children as they got older. But it plummeted in the 39 children who had experienced multiple types of violence, Shalev said.
He hazarded a rough estimate that these children had lost perhaps seven to 10 years of life compared with children who had more tranquil lives.
"Kids who are raised in poverty and hardship have more disease. This might explain why," said Dr. Owen Wolkowitz, a psychiatrist at UC San Francisco who has studied the link between depression and telomere length in adults. He was not involved in the Duke study.
The Duke team has not yet evaluated whether the British children had developed health issues, Shalev said. They are in the process of collecting more DNA from the twins and looking for evidence of incipient health problems such as increased blood pressure or diabetes.
"We think the health problems will probably be seen in later life," he said.