either a cause or an effect of CPA life style. The issue of causality is particularly difficult in human studies although a parallel longitudinal analysis of behavioral and DNA methylation changes could have established at least the temporal relationship between differential DNA methylation of cytokines and aggressive behavior. In addition, childhood abuse or neglect is also known to increase the risk of aggression in adolescents and adults [85] and was also found to associate with DNA methylation differences [59]. Therefore, it is possible that child abuse acts as a third factor in explaining the reported association between aggression and DNA methylation.
