Review Question - QID 214350

A 55-year-old African American man presents to his primary care physician for fatigue. He has been feeling progressively tired over the course of 6 months. He sleeps approximately 10 hours a day and at times experiences shortness of breath with exertion. His diet consists of meats and vegetables, and he lives in an apartment complex constructed in 1979. He has a medical history of hypertension and hyperlipidemia. His mother suffered from anemia and uterine fibroids. Physical examination is notable for mild conjunctival pallor and delayed capillary refill. He has bilateral palmar erythema and normal proprioception and vibration sensation. Laboratory studies are shown:

Hemoglobin: 11.5 g/dL
Hematocrit: 35%
Mean corpuscular volume: 105 µm^3
Leukocyte count: 4,000 /mm^3 with normal differential
Platelet count: 200,000/mm^3

A peripheral blood smear is demonstrated in Figure A. Which of the following is most likely the cause of this patient's symptoms?