RFX6 and Melkersson-Rosenthal syndrome: Mitchell–Riley syndrome (MRS) is an autosomal recessive disorder caused by mutations in the RFX6 gene in which a combination of neonatal diabetes mellitus and congenital gastrointestinal defects—such as atresia, stenosis or malrotation of the small intestine, gallbladder hypoplasia or agenesis, intrahepatic or extrahepatic ductal atresia, or hypoplastic or annular pancreas—occur [1–6]. In a limited number of patients with MRS, heterotopic jejunal gastric mucosa, including in the duodenal and jejunal tract, has been described [2, 7, 8].