CLDN18 and Barrett esophagus: The change from a CLDN18-deficient tight junction in healthy squamous epithelium from subjects without oesophageal disease to a Cldn-18-rich tight junction in specialised columnar epithelium of Barrett’s oesophagus contributes to preventing the squamous epithelium from being attacked and destroyed by luminal acid, thereby promoting tumourigenesis (15, 75).