In search of genetic factors for pathophysiological basis of psychiatric disorders, recent large-scale genome-wide association studies (GWAS) have finally started showing promising results. However, the biological significance of the small effect sizes observed from these GWAS investigations is presently unknown. Epigenetics is thought to play an important role in gene and environment interaction. It therefore has the potential to provide a molecular basis by which traumatic or stressful life events trigger psychiatric disorders such as posttraumatic stress disorder or depression. Thus, the number of papers published on epigenetics and psychiatry has been exponentially increasing over the last one decade. Epigenetic processes including DNA methylation, histone modification, and micro RNA are involved in regulating gene expression. Of them, DNA methylation is the most widely studied. Due to recent advancement in genomics research technology, epigenetics research has shifted from the traditional candidate gene approach to the more comprehensive genome-wide approach. Cumulative results from epigenetic research suggest that epigenetic mechanisms are involved in regulating human behavior by altering endocrinological and physiological functions. As such, epigenetic modifications may also be a promising candidate involved in treatment response of patients diagnosed with psychiatric disorders.
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