Sideroblastic anemia Quiz: Ace Your Exams

A 44-year-old man comes to the primary care PA complaining of fatigue and shortness of breath for the past several weeks. He lives in a 2nd floor apartment and has difficulty catching his breath after climbing the stairs. He also reports feeling tingling in his hands and feet during this same time period. The patient recently immigrated from India and was being treated for a disease with a daily medication, but cannot recall its name. He has no cognitive impairment, abnormal bleeding episodes, or depression. Temperature is 37.0°C (98.6°F), pulse is 94/min, respirations are 14/min, and blood pressure is 124/78 mmHg. Physical examination shows conjunctival pallor. There is diminished sensation bilaterally on the hands and feets. Laboratory investigations show a hemoglobin of 9.4 g/dL (reference range: 13.5-17.5 g/dL). Bone marrow biopsy reveals numerous hypochromic erythrocytes with coarse basophilic granules, which are positive for Prussian blue staining. Reduced activity of which of the following enzymes is likely responsible for this patient’s condition?