SLC6A4 and irritable bowel syndrome: After the evaluation of eleven candidate SNPs, our study identified five IBS-associated polymorphisms that were involved in neuro-immune signal pathways: TNFSF15 rs4263839 (cytokines system), ADRA1D rs1556832 (adrenergic system), COMT (rs4680, rs6269), SLC6A4 5-HTTLPR (serotonin reuptake transporter), and HTR3A rs1062613 (serotonin system).