Endothelin and leptin within serum, and myeloperoxidase and midkine within urine, seemed to be more involved in women’s MDD pathophysiology, whereas apolipoprotein A1, EGF and myeloperoxidase within serum and cortisol, substance P and thromboxane B2 seemed to be more involved within men′s MDD pathophysiology. This evidence concerns the gene MPO and major depressive disorder.