Causes include absolute or functional iron deficiency, inflammation, infection, lack of dialysis adequacy, hyperparathyroidism, hemolysis, nutritional factor deficiencies, aluminum overload, pure red cell aplasia, malignancy, bone marrow disorders, myelosuppressive agent use, and use of angiotensin converting enzyme inhibitors and angiotensin receptor blockers. The gene discussed is ACE; the disease is hyperparathyroidism.