IBS is characterized by aberrant gut motility and visceral hypersensitivity that collectively contribute to bouts of diarrhea and constipation and heightened pain perception during digestion and bowel movements (169) IBS patients may express lower levels of SERT, and certain SERT alleles may present an increased risk for developing IBS and other 5-HT-related pathologies, though this finding is inconsistent across studies (29, 170, 171). The gene discussed is SLC6A4; the disease is irritable bowel syndrome.