5-HT signaling is ultimately terminated through uptake by serotonin reuptake transporter (SERT) across the plasma membrane where 5-HT is broken down into 5-hydroxy indoleacetic acid (5-HIAA) by monoamine carboxylase.102 Admittedly, quantifying effects of 5-HT on visceral hypersensitivity in IBS has proven challenging. Here, SLC6A4 is linked to irritable bowel syndrome.