FKBP4 and post-traumatic stress disorder: After adverse life events, variants for FKBP5, the human gene that encodes FKBP51 (Human Gene Organization [HUGO] nomenclature), influence risk for subsequent PTSD (Binder et al., 2008; Boscarino et al., 2012; Hawn et al., 2019; Klengel et al., 2013; Li et al., 2019; Watkins et al., 2016; Xie et al., 2010; Zhang et al., 2020) and depression (Appel et al., 2011; Dackis et al., 2012; Zimmermann et al., 2011).