The A20 gene locus has been associated with risk for Crohn's disease, systemic lupus erythematosus, rheumatoid arthritis, type I diabetes, psoriasis, and atherosclerosis. A20 is an important regulator of autoimmunity and a tumor suppressor for Hodgkin's lymphoma and large B cell lymphoma. A20 acts through the transcription factor nuclear factor-κB (NF-κB) to control inflammation, and NF-κB regulates the expression of genes involved in inflammation and immunity. The gene discussed is TNFAIP3; the disease is Crohn disease.