SLC6A4 and irritable bowel syndrome: Both l and xl alleles of 5-HTTLPR in the SLC6A4 gene were found more common in IBS participants, and the s allele was the major allele in the HC group in our study, while the s allele of SLC6A4 5-HTTLPR and l allele were considered the risk allele of IBS in two other studies, respectively [52,53].