RETN and major depressive disorder: For example, one study of 36 patients with MDD showed that a compositive biomarker test—comprising nine individual biomarker assays (α1 antitrypsin, apolipoprotein CIII, myeloperoxidase, soluble tumor necrosis factor α (TNFα) receptor type II, epidermal growth factor, cortisol, brain-derived neurotropic factor, prolactin, and resistin)—had 91.7% sensitivity and 81.3% specificity for MDD [6].