BDNF and bipolar disorder: Val66Met in the BDNF gene was indeed associated with bipolar disorder in the European population (odds ratio = 1.14; 95% CI = 1.04–1.23; p = 0.0029; I2 = 49.3%; 15 case–control samples and 4 family-based samples; 11,723 patients and 12,312 controls) but not in the Asian population (odds ratio = 0.97; 95% CI = 0.91–1.04; p = 0.443; I2 = 6.7%; 11 case–control samples; 3,324 patients and 3,314 controls).