To interpret the significant interaction between methylation and hippocampal volume, we ran correlation analyses between hippocampal volume and GR methylation on the participants that are likely to have met diagnostic criteria for PTSD (i.e., PCL-C > 50, n = 38) and those who likely do not (50 and below, n = 29) in accordance to previously published recommendations [32, 33] (see Fig 2). Here, NR3C1 is linked to post-traumatic stress disorder.