JAK2 and inflammatory bowel disease: Recent genome-wide association studies (GWAS) have identified 163 host genetic loci which show significant association with IBD, and these genes can be classified into several key pathways including innate immunity (e.g., NOD2), cytokine signaling (e.g., JAK2, STAT3, and TYK2), and the maintenance of intestinal barrier integrity (e.g., HNF4A, CDH1, and MUC19) [1, 2].