Using baseline data, after controlling for age, educational years, and duration of MDD, partial correlation analysis yielded that occupational functioning was negatively associated with serum GDNF levels (r (79) = -0.24, 95% CI = [–0.43, –0.02], p = 0.033) in all FEDN MDD patients, see Figure3A. This evidence concerns the gene GDNF and major depressive disorder.