Two new studies are pointing to a genetic link between traumatic events, chronic pain and post-traumatic stress disorder (PTSD).
One study found a higher risk for PTSD in soldiers exposed to childhood trauma, while the other found that people who experience trauma while living in low-income neighborhoods are more likely to suffer from musculoskeletal pain. Both studies suggest that trauma can “activate” genes associated with chronic pain.
“We all like to believe that we are immune to the circumstances of our environment,” said lead author Samuel McLean, MD, associate professor of anesthesiology and emergency medicine at the University of North Carolina School of Medicine.
“These results suggest that when it comes to chronic musculoskeletal pain development after traumatic/stressful events, the poet John Donne was right – ‘No man is an island.’ ”
Mclean’s study, published online in the journal Pain, followed 948 Americans for a year after they were treated at emergency rooms in four states after car accidents. Researchers found that patients living in disadvantaged economic areas were more likely to be in pain months after the accident. The results remained significant even after adjusting for other risk factors such as age, education, opioid use, obesity, and mental health status prior to the accident.
Researchers say there are many ways that living in a poor neighborhood might increase pain after a car accident. One potential factor is that living in a disadvantaged neighborhood increases an individual’s stress or “fight or flight” response.
To test this theory, researchers collected blood samples from patients and evaluated whether those with a common genetic variant which makes one more vulnerable to stress were more affected by pain. The investigators found that was the case; those without the genetic variant were relatively unaffected by pain, while those with the gene had large and clinically significant differences in pain outcomes depending on their neighborhood.
“This finding suggests that the increased stress of living in a disadvantaged neighborhood affects biological systems in the body in ways that increase pain and worsen pain outcomes,” said Dr. McLean. “These results also add further evidence that stress systems are involved in the development of chronic pain. This is really important, because we have to understand the biology in order to be able to develop better preventive interventions.”
Childhood Trauma and PTSD
A study by researchers at Columbia University’s Mailman School of Public Health and the University of Michigan also found an association between genes and childhood trauma.
The study, published online in JAMA Psychiatry, looked at 810 Ohio National Guard soldiers of European descent who reported having a traumatic event in their lives. Nearly three-quarters of the guardsmen had been deployed to combat zones, including Iraq and Afghanistan, and 42% had seen active military combat.
Service members were asked about their childhood exposure to physical, sexual, or emotional abuse, or if they witnessed domestic violence between their parents. Soldiers were also asked about their adult trauma, including 33 categories of deployment-related and non-deployment events, and then they were evaluated for PTSD symptoms.
A control group of predominantly African-American female civilians in Atlanta was also evaluated for childhood adversity, adult trauma, and PTSD symptoms in a similar fashion.
The researchers found “strong evidence” in both groups that subjects with the ADRB2 gene – which is believed to play a role in chronic pain – were more likely to have PTSD if they had two or more childhood traumas.
“Of particular note is the finding that the identical interaction took place in the control group of civilians. Together these outcomes suggest that the ADRB2 gene interacts with childhood adversity and either result in a vulnerability or resilience to developing PTSD symptoms following adult trauma,” said senior author Sandro Galea, MD, chair of Epidemiology at the Mailman School of Public Health.
Soldiers with the AA genotype of the ADRB2 gene were least likely to have adult PTSD symptoms; those with the AG genotype had an intermediate risk of adult PTSD symptoms; and those with the GG genotype had the greatest risk of adult PTSD symptoms.
No differences were observed for those with less than two types of childhood trauma.
“Our findings that the ADRB2 factor might be shared by men and women, African Americans and European Americans, and military and civilians is consistent with the idea that some genetic risk factors for PTSD might be common across populations and even shared by other stress-related disorders, such as depression,” said Galea.
Lifetime exposure to trauma was also a strong predictor of PTSD symptoms, regardless of the genotype. This was expected since epidemiologic studies have identified severe trauma exposure as a major risk factor for PTSD. Significant interaction between genetic variance and adult trauma alone was not observed.
“This suggests that genetic variance in interaction with childhood trauma alone can influence adult PTSD symptom severity,” said Galea.
“By understanding how PTSD develops, we are better positioned to employ effective prevention and intervention strategies in the military and beyond,” said Israel Liberzon, MD, University of Michigan Professor of Psychiatry and first author of the study. “With these data, we will help patients suffering from the strains of PTSD earlier on, and prevent unnecessary pain, suffering and stress.”
A recent survey by National Pain Report found that seven out of 10 women with chronic pain had one or more incidents of childhood trauma. Nearly half the women had experienced emotional abuse as children.
Although many health professionals believe there is an association between childhood trauma and chronic pain, over half the women surveyed do not believe their pain is linked to physical or emotional trauma.