Chronic granulomatous disease (CGD) results in recurrent infections due to impaired killing of catalase-positive organisms. The underlying defect involves which component of the NADPH oxidase complex?

• A Myeloperoxidase — the granule enzyme for HOCl generation
• B Lactoferrin — the iron-chelating protein in secondary granules
• C Defensins — the antimicrobial peptides in azurophil granules
• D gp91phox (CYBB) — the membrane-bound catalytic subunit ✓

Explanation

The most common form of CGD (X-linked, ~65% of cases) involves mutations in CYBB encoding gp91phox, the beta subunit of cytochrome b558, which is the electron-transferring catalytic core of NADPH oxidase. Lack of functional NADPH oxidase prevents superoxide (O2-) and downstream reactive oxygen species generation, impairing killing of catalase-positive bacteria (Staphylococcus, Aspergillus, Serratia). These organisms detoxify their own H2O2 with catalase, so only the respiratory burst matters. Myeloperoxidase deficiency is usually mild; lactoferrin and defensins are not the primary defect in CGD.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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