While it is not surprising that many survivors developed post traumatic stress disorder (PTSD), not all of them did. However, why such a situation should be so has also been disturbing researchers for the last 16 years. PTSD is an anxiety disorder that can occur when we experience or witness a life-threatening event such as abuse, natural disaster and war.
Dr Iris-Tatjana Kolassa, from the department of Clinical Psychology and Neuropsychology at the University of Konstanz in Germany, and other colleagues in Germany and Switzerland – decided to look for some answers by applying their knowledge of molecular genetics.
Available statistics suggest that although there is no exact official figure, estimates show that 1 in 5 of the population of Rwanda, or up to 1 million people lost their lives in the 1994 genocide, which occurred over about 100 days.
As anticipated, the researchers found a “dose-response” relationship between traumatic load and prevalence of lifetime PTSD. This means that the higher the traumatic load, the higher the chance of developing PTSD, according to Dr. Kolassa, writing in the journal Biological Psychiatry.
But they also found something else: a variant of a gene that codes for the enzyme catechol-O-methyltransferase (COMT) appears to play a role in this relationship. The variant is called the COMT Val158Met polymorphism and has already been implicated in previous studies that linked it to fear extinction.
Carriers of the Met/Met version of the gene (ie they inherited Met from both parents) showed a high risk of developing PTSD independently of their traumatic load, whereas carriers who had at least one Val version of the gene, showed the expected dose-response relationship between traumatic load and risk of developing PTSD.
The COMT enzyme metabolizes the neurotransmitters norepinephrine and dopamine which are released during stress, and the researchers suggested that the Met/Met carriers had substantially lower activity of COMT enzyme, leaving them more vulnerable to PTSD independently of traumatic load.
Dr. John Krystal who edits Biological Psychiatry said he hoped molecular genetics studies like this “will help us learn more about resilience so we can help people cope with stress at psychological, behavioral, and biological levels”.
“We also would like a biological test to help us to identify people who are most vulnerable to the negative effects of stress so that we could target supportive services to these people,” he added.
Kolassa was more cautious. She said they have to deal with many unanswered technical and clinical questions “before we can start thinking about developing molecular genetic tests that predict patterns of stress response”.
But she added that the team expects that one day molecular genetics will play a key role in helping to prevent and treat PTSD.
For the study, they examined samples and medical records from 424 Rwanda Genocide survivors living in the Nakivale refugee camp in southwestern Uganda, some with and some without PTSD.
About the study: “The Risk of Posttraumatic Stress Disorder After Trauma Depends on Traumatic Load and the Catechol-O-Methyltransferase Val158Met Polymorphism.” Biological Psychiatry, Volume 67, Issue 4, 15 February 2010, Pages 304-308