They demonstrated that Val66Met in the BDNF gene was not associated with MDD in European (odds ratio = 1.00; 95% confidence interval (95% CI) = 0.93–1.09; p = 0.69; I2 = 48.4%; 24 case–control samples; 15,419 patients and 29,007 controls) and Asian (odds ratio = 0.97; 95% CI = 0.89–1.06; p = 0.535; I2 = 37.2%; 13 case–control samples and 1 family-based sample; 7,371 patients, 8,742 controls, and 105 trios) populations. Here, BDNF is linked to major depressive disorder.