Vitamin B12 deficiency becomes important in high-risk populations such as the elderly, patients with either malabsorption diseases as in gastric and ileal resection or gastric mucosal disease resulting from either an autoimmune process or from gastric atrophy, pancreatic insufficiency, coeliac disease, Crohn's disease, ileitis, vegetarians and long-term use of proton pump inhibitors [4], histamine (H2) receptor antagonists [5], or biguanides [6, 7]. The gene discussed is HRH2; the disease is Crohn ileitis.