A clinical study of adult patients with chronic bloody diarrhea is performed. One group of these patients is found to have a statistically increased likelihood for the following: antibodies to Saccharomyces cerevisiae but not anti-neutrophil cytoplasmic autoantibodies, NOD2 gene polymorphisms, TH1 and TH17 immune cell activation, vitamin K deficiency, megaloblastic anemia, and gallstones. Which of the following diseases is this group of patients most likely to have?

These are findings of idiopathic inflammatory bowel disease most likely to be Crohn disease. The ileal involvement accounts for vitamin K and vitamin B12 deficiencies as well as disrupted enterohepatic circulation of bile salts predisposing to gallstone formation. The inflammatory response in Crohn disease may result from inappropriate innate immune responses to gut flora, as discussed in the text. Angiodysplasia leads to bleeding from abnormal submucosal vessels, most often in the cecum of older adults. Diverticular disease is common in older persons but results from mechanical, not immune, mechanisms. Severe peripheral atherosclerosis may cause ischemic bowel disease, but this is usually an acute process.