COMT and major depressive disorder: In other systems, genotype (e.g., polymorphisms in the serotonin transporter gene, cannabinoid receptor 1, or catechol-O-methyltransferase) can significantly influence behavior such as depression, suicide attempts, hazardous drinking, and posttraumatic stress disorder, but only after an increased number of stressful life events or high traumatic load [71], [72], [73], [74].