These include carriage of the apolipoprotein E ɛ4 allele (Geroldi et al., 2000) and mood disorders, including posttraumatic stress disorder (Pavic et al., 2007), bipolar disorder (Haukvik et al., 2014), major depression (Mathias et al., 2016), and anxiety (Levita et al., 2014). Here, APOE is linked to bipolar disorder.