Papakostas et al. (2013) [18] and Bilello et al. (2015) [62] used a panel of nine serum markers that were also measured in our study (α1-antitrypsin, apolipoprotein CIII, brain-derived neurotrophic factor, cortisol, epidermal growth factor, myeloperoxidase, prolactin, resistin and TNFR2) to achieve a test accuracy of 91% (AUC = 0.93) in separating MDD patients from controls. This evidence concerns the gene RETN and major depressive disorder.