Can leave a traumatic imprint (Image: Joe Raedle/Getty)

Traumatic experiences can scar for life, both mentally and physically. Now it seems they even leave chemical marks on DNA – in areas responsible for immune functions and memory.

The result could help explain why people with post-traumatic stress disorder (PTSD), including some soldiers and victims of rape or earthquake, often have poorer physical health years later, as well as memory problems. It could also lead to a new method for diagnosing the disorder.

Sandro Galea and his team at Columbia University, New York, looked at blood samples from 23 people who had PTSD and 77 who didn’t. Galea examined the samples to see if there were any notable differences in the levels of methyl groups that were attached to various genes.


Such “epigenetic” chemical changes don’t change the genetic code, but can mean that a gene’s function is increased or decreased, or switched on or off.

Weak immunity

The team identified a number of genes with altered methylation in people with PTSD – all of which were involved in immune function and brain cell development. This might explain why PTSD sufferers have weaker immune systems and poorer memories, says Galea.

What’s more, the number of affected genes was linked to the number of traumatic events a person with PTSD had experienced. “We think that traumatic events induce methylation changes,” says Galea.

The people with PTSD also had more antibodies to cytomegalovirus (CMV), a herpes virus that is present to some degree in most human populations. This indicates that their levels of CMV were higher, and greater CMV infection is associated with an ageing immune system.

“It is tempting to speculate that higher CMV antibodies observed in PTSD could be a hallmark of accelerated ageing features associated with psychological stress exposure,” says Moisés Bauer at the Pontifical Catholic University of Rio Grande do Sul in Porto Alegre, Brazil.

Diagnosing trauma

Galea says he hopes his team’s findings will help those with PTSD. For a start, changes in methylation might help diagnose the condition. “It’s not implausible that epigenetic changes could provide a biomarker, a diagnostic tool for PTSD,” he says.

“It will also help guide us on interventions,” he says. Galea hopes to find a way of preventing the epigenetic changes in individuals who have recently experienced traumatic events. Bauer agrees: “Drugs targeting DNA methylation profiles will be of clinical interest for PTSD.”

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0910794107