Previous studies have shown effects of early life adversity on overall higher methylation in SLC6A4 promoter in adults who were adopted in infancy (Beach et al., 2010) and in patients with major depression (Kang et al., 2013) and bipolar disorder (Sugawara et al., 2011; Zhao et al., 2013). This evidence concerns the gene SLC6A4 and bipolar disorder.