UC: ulcerative colitis; CD: Crohn's disease; PR3-ANCA: antineutrophil cytoplasmic antibodies specific for proteinase-3; ANCA: antineutrophil cytoplasmic antibodies; IBD: inflammatory bowel disease; MPO-ANCA: myeloperoxidase-associated antineutrophil cytoplasmic antibodies; TNF-α: tumor necrosis factor alpha; ASCA: anti-Saccharomyces cerevisiae antibody; CRP: C-reactive protein; PSC: primary sclerosing cholangitis. The gene discussed is MPO; the disease is inflammatory bowel disease.