Considering that IL-1β and PGE2 are potential triggers of depression (Müller et al., 2006; Goshen and Yirmiya, 2009), and that LTB4 is able to repress the production of these mediators (Zoccal et al., 2016), we hypothesized that 5-LO deficiency would increase the susceptibility to depression. This evidence concerns the gene ALOX5 and major depressive disorder.