Recently, a case-control study reported that patients with depression have lower levels of brain-derived neurotrophic factor (BDNF) and increased expression of microRNA-132 and microRNA-182, when compared with healthy subjects, suggesting that serum BDNF and the related microRNAs can be used as biomarkers for diagnosis or as therapeutic targets of depression (Li et al., 2013). Here, BDNF is linked to major depressive disorder.