In our previous study, we reported that the disturbance of serum tPA-BDNF pathway was related to the pathogenesis of MDD, and the combination of tPA, BDNF, proBDNF, TrkB and p75NTR, the factors found in the pathway, could improve diagnostic power from a single protein for MDD diagnosis21. This evidence concerns the gene NTRK2 and major depressive disorder.