Posttraumatic stress disorder (PTSD) is a common and debilitating mental disorder that occurs in some individuals following a traumatic event. It includes symptoms such as reexperiencing the event, avoidance of event-related stimuli and chronic hyperarousal. In the United States, 1 in 9 women and 1 in 20 men will meet criteria for the diagnosis at some point in their lives.1 The societal impact of PTSD is large, with increased rates of suicide, hospitalization and substance use.2 Regarding etiology, the role of nature versus nurture in response to traumatic events has been debated for over a century.3 Psychiatrists who treated ‘shell shock’ in soldiers returning from World War I argued over whether soldiers who succumbed to the stressors of war were ‘moral invalids’ or whether such breakdowns could occur in any man who was ‘buried in a trench or saw his friend’s brains scattered before him’.4 This historical controversy has been reignited as the age of genomic medicine has reached PTSD. Genomic research is given the highest priority in the US National Research Action Plan on PTSD that was established in
