Growing evidence points to a role of epigenetic alterations in the development of psychiatric disorders. DNA methylation – an epigenetic mechanism sensitive to both genetic and environmental influences – has been linked to a wide range of emotional and behavioral problems in childhood, including anxiety, depression, conduct problems and attention-deficit hyperactivity. However, findings to date have been primarily drawn from candidate gene studies, or EWAS studies investigating single sites across the genome. As a result, how much of the variance in psychiatric phenotypes is collectively explained by the methylome as a whole is currently unknown.