MUC19 and inflammatory bowel disease: Numerous genetic studies highlight that many susceptibility genes of irritable bowel disorder (IBD) are involved in maintaining the integrity and normal functions of the intestinal barrier, such as mucus and glycoprotein regulation (MUC19) [27], MUC3 [28], epithelial differentiation (HNF4a) [29], and membrane transport (ITLN1) [30].