Review Question - QID 109818

A 7-year-old boy presents to the emergency department with sudden pain that started suddenly in his hands 1 hour ago. He has not eaten anything new lately. He did play football earlier this morning and admits to being tackled forcefully multiple times. The child is doing well in school and is proud that he has a new girlfriend. The child has a medical history of obesity and is not currently on any medications. His temperature is 100°F (37.8°C), blood pressure is 120/68 mmHg, pulse is 100/min, respirations are 11/min, and oxygen saturation is 98% on room air. Cardiopulmonary exam is within normal limits. On physical exam of the patient's extremities, there is painful and symmetrical swelling of his hands and feet but no rashes are present. The patient is started on analgesics. He is noted to have a hemoglobin of 8.0 g/dL. Which of the following is the most likely cause of this patient's presentation?