A 20-year-old woman has recurrent infections with Candida albicans and Staphylococcus aureus. Neutrophil counts, phagocytosis, and oxidative burst generation are all normal, but intracellular killing after ingestion is defective. The most likely enzyme deficiency is:

• A NADPH oxidase
• B Glucose-6-phosphate dehydrogenase
• C Myeloperoxidase ✓
• D Superoxide dismutase

Explanation

Myeloperoxidase converts hydrogen peroxide and chloride into hypochlorous acid inside the phagolysosome. In MPO deficiency the oxidative burst still generates superoxide and hydrogen peroxide normally, but halogenation and intracellular killing are impaired, leading to candidal and staphylococcal infections. NADPH oxidase deficiency defines chronic granulomatous disease and abolishes the burst itself, which is normal here, ruling out option A.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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