For example, Abu-Farsak et al. [108] found there was a positive correlation between the expression of Claudin-2 and TGR5 in the esophageal tissue, and the expression levels of claudin-2 were significantly increased from normal squamous mucosa to columnar cell metaplasia, Barrett's esophagus, and low- and high-grade dysplasia to esophageal adenocarcinoma. The gene discussed is CLDN2; the disease is Barrett esophagus.