Recent studies have highlighted that epigenetic modifications in clock and other genes (different degrees of methylation) can contribute to the development of depression and anxiety disorders during the perinatal period [25], as a result of hypomethylation of clock genes CRY1 and CRY2 [9] and modulation of HERV-W, the latter implicated in maternal immune tolerance during pregnancy [26]. Here, CLOCK is linked to anxiety disorder.