This finding has potential implications for vulnerability to mental disorders in humans, given that increased OXTR DNA methylation in exon III has been linked to autism spectrum disorder (Gregory et al., 2009), psychopathy (Dadds et al., 2014), obsessive-compulsive disorder (Cappi et al., 2016), depression (Chagnon et al., 2015), and anxiety disorder (Ziegler et al., 2015). Here, OXTR is linked to major depressive disorder.