SLC6A4 and irritable bowel syndrome: However, any dysfunction in SERT causes an imbalance in the level of 5-HT and affects the intestinal function, including the intestinal fluid secretion, intestinal motility, and GI perception, decrease expression of SERT in the gut is implicated in subsets of irritable bowel syndrome (IBS), therefore SERT plays a pivotal role in IBS pathogenesis43,44.