Attempts to identify the genetic causes of neuropsychiatric diseases such as post-traumatic stress disorder (PTSD) through large-scale genome-wide analyses have yielded thousands of potential links. The challenge is further complicated by the wide range of symptoms exhibited by those who have PTSD. For instance, does extreme arousal, anger, or irritation experienced by some have the same genetic basis as the tendency to re-experience traumatic events, another symptom of the disorder?