A child has recurrent infections with Staphylococcus aureus and Candida albicans. Neutrophils phagocytose organisms normally and show a normal respiratory burst, but fail to kill ingested microbes inside the phagosome. The most likely defect is:

• A NADPH oxidase deficiency
• B Defective lysosomal enzyme packaging
• C CD18 integrin deficiency
• D Myeloperoxidase deficiency ✓

Explanation

Myeloperoxidase converts hydrogen peroxide plus chloride into hypochlorous acid within the phagolysosome. In MPO deficiency the respiratory burst is intact, so superoxide generation is normal, but the halogenation step fails and intracellular killing of staphylococci and especially Candida is impaired. NADPH oxidase deficiency abolishes the burst itself, which distinguishes chronic granulomatous disease from this case, and CD18 defects impair adhesion rather than killing.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.