NHE3 activity is decreased in IBD patients, either because of decreased NHE3 protein levels as found in both UC and CD patient biopsies (Sullivan et al., 2009) with reduced NHE3 mRNA seen only in CD biopsies (Siddique et al., 2009), or independently of its expression, i.e., without any changes in mRNA, protein and surface expression levels as found in biopsies of UC patients (Farkas et al., 2010; Yeruva et al., 2010; Yeruva et al., 2015). This evidence concerns the gene SLC9A3 and irritable bowel syndrome.