Neuroendocrinologic studies have reported three common features in patients with PTSD: (1) decreased plasma cortisol; (2) higher CRH in the cerebrospinal fluid (CSF) and plasma; and (3) increased inhibition of the hypophysis-adrenal system (HAS), which leads to reduced cortisol levels by enhancing negative feedback (Carvalho et al., 2008). This evidence concerns the gene CRH and post-traumatic stress disorder.