Dysregulation of catecholaminergic signaling has been implicated in the etiology of IBS, as supported by reports that SNPs within two catecholaminergic signaling pathway genes, Catechol-O-methyltransferase [23] and alpha adrenergic-1D (ADRA1D), are associated with IBS symptom severity [24]. Here, COMT is linked to irritable bowel syndrome.