Population-based longitudinal studies show that higher levels of CRP and IL-6 at baseline are associated with an increased risk of depression in subsequent follow-ups (Gimeno et al., 2009; Wium-Andersen et al., 2013; Khandaker et al., 2014; Zalli et al., 2016), suggesting that inflammation could be a cause rather than simply a consequence of the illness. This evidence concerns the gene IL6 and depressive disorder.