We also note that, despite a potential “healthy soldier effect”, both veterans and civilians with PTSD exhibit the altered DNA methylation status in hypothalamic–pituitary–adrenal (HPA) axis regulatory genes such as NR3C1. Genes associated with sleep (PAX8; LHX1) are seen to be differentially methylated in veterans. This evidence concerns the gene NR3C1 and post-traumatic stress disorder.