Although the present study aimed at elucidating the associations of the OPRM1 polymorphism with depression vulnerabilities, from a broader perspective it provides further evidence for the implication of MOR in social bonding behaviors (Burkett et al., 2011; Machin & Dunbar, 2011; Moles et al., 2004; Nummenmaa et al., 2015). This evidence concerns the gene OPRM1 and major depressive disorder.