STAT1 and inflammatory bowel disease: Gastrointestinal symptoms may occur in patients with STAT1 GOF-mutations, and endoscopies performed showed intraepithelial lymphocytosis in the duodenum of P1 and P2, atrophic gastritis in P2 and P3, and a severe inflammatory bowel disease starting in childhood for P3, with deep ulcerations in the esophagus and throughout colon.