Additional candidate genes identified to interact with environmental risk include GABRA2 and child abuse (8), APOE and combat exposure (9), ADRB2 and childhood trauma (11), CNR1 and child abuse (103), and COMT, a key player in catecholamine catabolism, where traumatic load modified PTSD susceptibility differentially in individuals with COMT polymorphisms (104). The gene discussed is COMT; the disease is post-traumatic stress disorder.