COMT and post-traumatic stress disorder: With respect to the interactive influence of COMT gene variation and life events in anxiety, only few gene-environment interaction (GxE) studies are available: Kolassa et al. [78] reported a GxE interaction of the Val158Met polymorphism and traumatic events in the etiology of posttraumatic stress disorder, with val allele carriers showing a trauma quantity dependent disease risk, while met homozygotes exhibited a high risk for PTSD independently of the severity of traumatic load.