One week prior to his hospital admission, he had a surveillance colonoscopy demonstrating progression of his Crohn’s disease, and therefore started on azathioprine 125 mg daily after routine testing of thiopurine methyltransferase (TPMT) levels were found to be intermediate at 38 nmol/g Hb/h (Intermediate: 10–40, Normal > 40). This evidence concerns the gene TPMT and Crohn disease.