FKBP5 and post-traumatic stress disorder: (v) PTSD-related genes: genetic activity related to the HPA axis, the noradrenergic system, and the limbic amygdala frontal pathway, such as FKBP5 polymorphism and demethylation, has been found to mediate fear processing in PTSD-related gene studies (Kang et al., 2019; Yun et al., 2022).