Principal investigator Dr. Sandro Galea of the Mailman School of Public Health at Columbia University and colleagues analyzed the methylation patterns -- which alter the gene pattern in cells that "remember where they have been" -- of more than 14,000 genes from blood samples of 100 Detroit residents, 23 with PTSD.
The study found that participants with PTSD had six to seven times more unmethylated genes than unaffected participants, and most of these unmethylated genes were involved in the immune system.
People who experience severe trauma exhibit a normal stress response, but the researchers suggested that with PTSD, the stress response system becomes deregulated and chronically overactive resulting diminished immune functioning.
"Our findings suggest a new biological model of PTSD in which alteration of genes, induced by a traumatic event, changes a person's stress response and leads to the disorder," Galea said in a statement.
The findings are published online in the Proceedings of the National Academy of Sciences.