A 3-year-old child presents with recurrent bacterial infections (Staphylococcus aureus, Aspergillus), lymphadenitis, and hepatomegaly. NBT (nitroblue tetrazolium) test shows failure of dye reduction by neutrophils. Dihydrorhodamine (DHR) flow cytometry confirms absent oxidative burst. The defect is in which molecular complex?
- A Myeloperoxidase in neutrophil azurophilic granules
- B NADPH oxidase (NOX2) complex ✓
- C Complement receptor 3 (CR3/CD11b/CD18)
- D Toll-like receptor 4 (TLR4) signalling pathway
Correct answer: B. NADPH oxidase (NOX2) complex
Explanation
Chronic granulomatous disease (CGD) results from deficiency of NADPH oxidase (NOX2 complex), which generates superoxide radical essential for killing catalase-positive organisms (Staphylococcus, Aspergillus, Serratia, Nocardia, Burkholderia). Failure to reduce NBT dye and absent DHR fluorescence confirms the absent oxidative burst. The most common form is X-linked (gp91phox subunit mutation). Myeloperoxidase deficiency is usually asymptomatic. CR3 deficiency causes leukocyte adhesion deficiency (LAD), with absent pus formation and umbilical cord delay.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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