COMT and major depressive disorder: One study found that COMT Val158 was significantly associated with a higher incidence of post-traumatic stress disorder 6 months after mild TBI.12 Conversely, COMT Val158 was not a significant predictor of depression 1 year after severe TBI.20 The association of COMT Val158 with emotional distress after moderate-severe TBI remains unclear and requires further investigation.