Similarly, a meta-analysis of studies evaluating the effect of the BDNF Val66Met polymorphism on major depressive disorder showed that, in the total sample, the BDNF Val66Met polymorphism is not significantly associated with depression; however, sex-stratified allelic and genotypic analyses revealed significant effects in men (Verhagen et al., 2010). This evidence concerns the gene BDNF and depressive symptom measurement.