A CpG site in the NPFFR2 gene was associated with total life stress, and plasma levels of interleukin (IL)-4, IL-2, and tumor necrosis factor-alpha were also associated with PTSD, child abuse, and total life stress, suggesting that psychosocial stress may be associated with peripheral immune dysregulation global and gene-specific DNA methylation patterns (Smith et al., 2011). Here, TNF is linked to post-traumatic stress disorder.