While GxE have been investigated on a genome-wide scale in genome-wide gene–environment interaction studies for a number of psychiatric phenotypes [18,19,20,21,22,23], studies of GxE in BD have, with a few exceptions, been limited to candidate gene approaches (e.g.: variation in BDNF, stressful life event, and worst episodes of depression and mania [24], childhood trauma and age of BD onset, severity, and chronicity [25]) and a handful of other GxE associations [26,27,28,29,30,31]—recently reviewed by Misiak et al. [32] and Musci et al. [33]). This evidence concerns the gene BDNF and Behcet disease.