BDNF and major depressive disorder: We have shown that the probability of developing FE can be estimated with a moderate predictive power using GDNF in LF and BDNF in BS; the probability of developing MDD can be estimated with a high predictive power using GDNF in LF, cortisol in BS, and TNF-α in BS, while the probability of developing FE with MDD can be estimated with a high predictive power using GDNF in LF, TNF-α in BS, and BDNF in BS.