A 30-year-old woman has recurrent infections with Candida albicans despite normal neutrophil count and normal phagocytosis. Neutrophil oxidative burst testing shows normal superoxide generation but absence of the respiratory burst's second phase. The defective enzyme is:

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

Explanation

Myeloperoxidase converts hydrogen peroxide and chloride ion into hypochlorous acid (HOCl), the most efficient microbicidal oxidant of the phagolysosome. In MPO deficiency the NADPH oxidase burst itself remains normal, but the H2O2-to-HOCl step fails, giving susceptibility particularly to Candida. NADPH oxidase deficiency defines chronic granulomatous disease, where the entire burst is abnormal, which separates the key distractor.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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