Q. An 84-year-old woman comes to your clinic with complaint of fatigue and dyspnea upon exertion for the past several months. You suspect that she is suffering from congestive heart failure and are surprised to find that on exam, her lungs sound clear. Regardless, you send her for an echocardiogram, which is normal. At follow-up, you appreciate that she does look more pale than usual. After inspecting her mucus membranes, you now suspect that she might be anemic. You order a series of iron studies, which demonstrate a microcytic anemia. Which of the following is NOT a cause of microcytic anemia?