The present study is the first report to show that each of the genetic factors, polymorphisms of IL-17F and TRAF3IP2, and the clinical risk factors, concomitant use of immunomodulators and penetrating disease, independently contributed to the therapeutic effect of IFX after the long-term (1 year) IFX treatment of Japanese CD patients. This evidence concerns the gene TRAF3IP2 and Cowden disease.