GDNF and major depressive disorder: From the results of receiver operating curve (ROC) analysis in PSD and MDD groups, the protein and mRNA levels of GDNF could serve as general distinguishing models with the AUC at 0.797 (95% CI, 0.696~0.898, P < 0.001) and 0.831 (95% CI, 0.744~0.918, P < 0.001) respectively (see Fig. 2).