SLC6A4 and irritable bowel syndrome: Case-control studies have examined the possible role of different SNPs in patients with IBS, such as serotonin transporter protein (SERT) [9], Catechol-O-methyltransferase (COMT) [10], β3 subunit of G-protein (GNβ3) [11], voltage-gated mechanosensitive Na(+) channel NaV1.5 (SCN5A) [12], and tumor necrosis factor (TNF)-α [13].