Among the PTSD samples, there were 8 COMT Met-BDNF Val/Val, 16 COMT Met-BDNF Met, 9 COMT Val/Val-BDNF Val/Val, and 22 COMT Val/Val-BDNF Met; within trauma-exposed controls, there were 16 COMT Met-BDNF Val/Val, 51 COMT Met-BDNF Met, 22 COMT Val/Val-BDNF Val/Val, and 66 COMT Val/Val-BDNF Met. This evidence concerns the gene COMT and post-traumatic stress disorder.