A 20-year-old woman has recurrent infections with Candida albicans and Staphylococcus aureus. Phagocytosis and oxygen radical generation are intact, and the nitroblue tetrazolium dye reduction test is normal, but neutrophil killing of ingested organisms is impaired. Which enzyme defect explains these findings?

• A NADPH oxidase
• B Myeloperoxidase ✓
• C Glucose-6-phosphate dehydrogenase
• D NADPH-dependent phagocyte oxidase p47phox subunit

Explanation

Myeloperoxidase converts hydrogen peroxide plus chloride into hypochlorous acid, the major microbicidal agent of the phagolysosome. In MPO deficiency the respiratory burst is intact, so the NBT test remains normal, distinguishing it from chronic granulomatous disease where NADPH oxidase failure gives an abnormal NBT result. Options A and D describe components of the same oxidase complex whose loss defines CGD, not this entity.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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