A number of human-based epigenetic studies of PTSD have been published (19–22), with the majority of them focusing on candidate genes which are chosen based on animal models or genetic association findings, such as NR3C1 (23, 24), FKBP5 (25, 26), SLC6A3 (27), and BDNF (28). This evidence concerns the gene BDNF and post-traumatic stress disorder.