A 4-year-old previously well African American boy is brought to the office by his aunt. She reports that he developed pallor, dark urine, and jaundice over the past few days. He stays with her, has not traveled, and has not been exposed to a jaundiced person, but he is taking trimethoprim-sulfamethoxazole for otitis media. The CBC in the office shows a low hemoglobin and hematocrit, while his stat serum electrolytes, blood urea nitrogen (BUN), and chemistries are remarkable only for an elevation of his bilirubin levels. His aunt seems to recall his 8-year-old brother having had an allergic reaction to aspirin, which also caused a short-lived period of anemia and jaundice. Which of the following is the most likely cause of this patient's symptoms?
a) G6PD deficiency
b) Hereditary spherocytosis
c) Hemoglobin C disease
d) Alpha-thalassemia