High-density mapping of the MHC identifies a shared role for HLA-DRB1*01:03 in inflammatory bowel diseases and heterozygous advantage in ulcerative colitis

John Rioux, Andre Franke, Tom Karlsen and colleagues perform a fine-mapping study of the HLA region in Crohn's disease and ulcerative colitis. They identify a primary role for HLA-DRB1*01:03 in both diseases and find evidence of heterozygous advantage in protection against ulcerative colitis.