However, changes in DNA methylation have been observed at several BD candidate gene loci such as serotonin system genes, brain-derived neurotrophic factor, and catechol-O-methyltransferase (Ghadirivasfi et al., 2011; Nohesara et al., 2011; D’Addario et al., 2012) in peripheral samples. Here, COMT is linked to Behcet disease.