COMT and irritable bowel syndrome: These include single nucleotide polymorphisms (SNPs) in genes related to signaling systems important in the control of gut motility or sensation in IBS, which includes serotoninergic (5-HT) system including tryptophan hydroxylase (TPH), serotonin reuptake transporter (SERT), a, cholecystokinin (CCK), voltage-gated sodium channels (Nav), Catechol-O-methyltransferase (COMT), cannabinoids, and ion channels, such as transient receptor potential (TRP) channels (TRPV1).