By Sara Jahnke
Are some people genetically predisposed to developing post traumatic stress disorder? As the research on genetics and biomarkers explodes, the answers seem to be yes, maybe, we think so, but we are not yet sure how exactly.
Most studies examining a genetic predisposition to PTSD have selected genes that are known (or at least believed) to be associated with the etiology, pathology or neurobiology of the disease. For PTSD, many genes are thought to be involved in the process, but the most frequently studied have to do with dopamine.
Dopamine is a chemical in the brain that regulates factors such as attention, arousal, sleep and feelings of vigilance. Neuroimaging studies find that there are often problems with the regulation of dopamine for people who have PTSD.
Studies estimate that people with some genetic profiles can be almost twice as likely as those without to experience PTSD.
One of the main challenges with this research, however, is taking into account the role the environment and other individual factors play. For instance, some studies find that certain genetic profiles are related to PTSD, but only among one gender while other studies find no relationship. Specific genes have been found to be significantly related to PTSD diagnosis, but only in specific ethnic groups.
Studies of twins that are either identical or fraternal suggest that almost half of the variability in risk can be estimated by genetic heritability. However, it also seems that being at risk for trauma may be linked to genetic factors.
For instance, studying identical male twins, they are twice as likely to both enlist in the military, which suggests maybe other genetic factors (like being more likely to be risk takers) may play an important role when considering risk factors.
Environmental and occupational factors that influence the physiology of the body also have been suggested as important to the development of PTSD.
Inflammation’s role
Dr. Anthony Walker from the University of Canberra Research Institute in Australia proposed a mechanism between mental health risks and inflammation in the journal Extreme Physiology and Medicine. He and his colleagues report that inflammation in the body has been found to be related to increased risk for PTSD and depression.
He proposes that part of the risks first responders face related to depression and PTSD are related to the physiological responses to occupational risks. For instance, one study among military personnel found that sleep disturbance was a precursor to PTSD and depression, which could be due to the inflammation caused by poor sleep.
Physical exhaustion, fatigue and inadequate time to recover (all issues first responders are at high risk for) also promotes inflammation and, quite possibly, PTSD.
Another source of inflammation may be related to heat exposure given the relationship between elevated core temperature and increased immune system activity. When studying firefighters during training, scientists have found increased levels of leukocytes, platelets and inflammatory activity.
Fine particulates like those present on the fireground and in diesel exhaust also can play an important role in that they promote inflammation in the lungs.
While some evidence suggests that high levels of cortisol likely are related to PTSD, research with firefighters and police has found that the chronic stressors firefighters face may also lead to chronically elevated cortisol levels. This long-term elevation is thought to lead to an inadequate cortisol response following trauma putting them at risk.
What may be even more interesting than the research about genes that may indicate a predisposition to the development of PTSD are the epigenetic effects of stress and trauma. The field of epigenetics explores how the expression of genes can be altered — basically how genes can be turned off or on — by factors such as lifestyle and the environment.
Gene switch
Dr. Monica Uddin from the University of Michigan and her colleagues studied the methylation of more than 14,000 genes among 23 individuals with PTSD and 77 people without. Methylation is the process by which methyl groups are added to genes either turning them off or on.
They found that those who had experienced a traumatic event and developed PTSD had altered immune function by reduced methylation on immune-related genes.
Research such as Dr. Uddin’s and others suggests that not only can genetics make people more or less likely to develop PTSD, but the experience of trauma may also impact genes by turning them off or on.
Estimates of lifetime prevalence of PTSD among first responders have been found to be two to three times higher than the general population. While the research is evolving, it is clear that it is not easy to predict who will get PTSD and that the development is due to a complex relationship between environmental, genetic and interpersonal factors.
It also seems likely that exposure to trauma changes the expression of genes among first responders who experience it on a daily basis.
While a definitive answer to the gene question is not in hand, the findings could eventually lead us to better understanding what causes PTSD, how to better treat it and how to prevent it.
About the author
Sara A. Jahnke, Ph.D. is the director of the Center for Fire, Rescue and EMS Health Research at the National Development and Research Institutes. She was the principal investigator on two large-scale, DHS-funded studies of the health and readiness of the U.S. fire service and on a study on the health of women firefighters. She is a co-investigator of several studies focused on fitness, nutrition and health behaviors in firefighters. She completed her doctorate in psychology with a health emphasis at the University of Missouri – Kansas City and the American Heart Associations’ Fellowship on the Epidemiology and Prevention of Cardiovascular Disease. You can reach her at Sara.Jahnke@firerescue1.com