Studies highlighted that different brain regions, like dentate gyrus (DG), dorsal DG, dorsal CA1, ventral CA3, basolateral amygdala, and medial prefrontal cortex, show different level of gene expression during the stress induction.62Roth et al reported that in PTSD, BDNF exon IV was hypomethylated in the ventral CA3 and no methylation changes observed in other hippocampal subregions in rats.63It is also reported in the literature that there is a relationship between the epigenetic status of catechol-O-methyltransferase and PTSD.64 The gene discussed is BDNF; the disease is post-traumatic stress disorder.