DEFA4 and major depressive disorder: The integrative analysis of the bioinformatics and ML identified 10 potent MDD-related biomarkers including CEACAM8, CLEC12B, DEFA4, HP, LCN2, NRG1, OLFM4, SERPING1, TCN1 and THBS1, that showed the most significant and strong differential expression between MDD patients and HCs.