This finding may be explained by the divergent expression of the serotonin transporter (SERT)/5-hydroxytryptamine (5-HT) system in IBS subtypes, with IBS-C revealing impaired 5-HT release and IBS-D characterized by reduced 5-HT uptake and upregulated SERT activity, resulting in improved intestinal mobility (29, 30). Here, SLC6A4 is linked to irritable bowel syndrome.