NR3C1 and post-traumatic stress disorder: A second study (Yehuda et al., 2013) evaluated 16 veterans with posttraumatic stress disorder (PTSD) in order to determine whether methylation of cytosine in the promoter region of GR gene NR3C1 and the FK506 binding protein 5 (FKBP5) gene (that codes for a co-chaperone protein of the GR) predicts response to prolonged exposure to psychotherapy (12 weeks).