USMLE Step 1 Question 305

Question:

An African American medical student goes to Central America on a medical mission trip. There, he develops weakness and dark urine soon after taking primaquine for antimalarial prophylaxis. This hemolytic reaction is likely due to:

Correct Answer: C.  Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate-dehydrogenase deficiency (Answer C) is the most common enzyme deficiency in the world. This erythrocyte deficiency is most prevalent among African and Mediterranean males. Without glucose-6-phosphate dehydrogenase, the pentose phosphate pathway is unable to produce NADPH. Without the reducing capability of NADPH, erythrocytes have no protection from oxidizing agents, thus leading to hemolysis. This X-linked recessive deficiency is often diagnosed when patients develop hemolytic anemia after receiving oxidizing drugs such as primaquine or after eating oxidizing substances such as fava beans.