In addition, the GDNF protein level in patients with MDD was lower than that in both PSD (FBonferroni = −45.758, SE = 9.460, P < 0.001, 95% CI, −71.059~−20.456) and non-PSD (FBonferroni = −36.217, SE = 9.283, P = 0.001, 95% CI, −61.046~−11.387) patients. This evidence concerns the gene GDNF and major depressive disorder.