FMO5 and inflammatory bowel disease: Both NOX1 and DOUX2 are epithelial NADPH oxidases involved in the generation of ROS in the gut epithelium.58 Mutations in NOX1 and DUOX2 result in reduced ROS production and cause a 10‐fold increase in bacterial invasion.59 Impaired mucosal defense may represent a key pathomechanism that results in intestinal inflammation and development of IBD.