A 5-year-old boy has recurrent infections with catalase-positive organisms including Serratia marcescens and Aspergillus. Nitroblue tetrazolium test is negative. Dihydrorhodamine flow cytometry shows no oxidative burst. Which component of the NADPH oxidase complex is most commonly defective?

• A p22-phox (membrane component)
• B p47-phox (cytoplasmic component)
• C gp91-phox (membrane component) ✓
• D p67-phox (cytoplasmic component)

Explanation

Chronic granulomatous disease is most commonly X-linked (65-70% of cases) due to mutations in CYBB encoding gp91-phox. Autosomal recessive forms involve p47-phox (NCF1, most common AR form), p67-phox, or p22-phox. The negative NBT and absent DHR flow cytometry confirm defective respiratory burst. Catalase-positive organisms survive inside neutrophils because they degrade their own H2O2, depriving the cell of substrate for the myeloperoxidase-H2O2-halide system.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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