A 30-year-old African man develops intravascular hemolysis and hemoglobinuria after taking primaquine. His RBCs show Heinz bodies on crystal violet staining. The enzyme deficiency responsible acts at which step of the hexose monophosphate (HMP) shunt?
- A Pyruvate kinase — final step of glycolysis
- B Glutathione synthetase — synthesis of reduced glutathione
- C Glucose-6-phosphate dehydrogenase — first committed step generating NADPH ✓
- D Methemoglobin reductase — reduction of ferric iron
Correct answer: C. Glucose-6-phosphate dehydrogenase — first committed step generating NADPH
Explanation
G6PD deficiency impairs the first step of the HMP shunt (pentose phosphate pathway), reducing NADPH generation. Without NADPH, glutathione cannot be maintained in its reduced form, leaving hemoglobin susceptible to oxidative denaturation into Heinz bodies, which cause membrane damage and intravascular hemolysis. Pyruvate kinase deficiency causes extravascular hemolysis with no Heinz bodies.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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