SLC6A4 and diarrheal disease: 5-HTT plays a key role in clearance of 5-HT by its rapid uptake to maintain optimal extracellular availability of 5-HT in the gut to facilitate its physiological actions and prevent receptor desensitization (Gill et al., 2013) In fact, several lines of evidence support downregulation of 5-HTT in inflammatory (Martel, 2006) or diarrheal disorders (Foley et al., 2007).