COMT and migraine disorder: Nevertheless, decreased risk of migraine was observed to be in association with COMT rs4680 polymorphism in overall analysis (AA vs. GG + GA: OR = 0.76, 95% CI = 0.60–0.97, PHet > 0.642, I2 = 0), and in Caucasian group after subgroup analysis (AA vs. GG + GA: OR = 0.75, 95% CI = 0.58–0.96, PHet > 0.433, I2 = 0).