A 6-year-old child presents with recurrent Staphylococcus aureus abscesses, eczema, and coarse facial features. A nitroblue tetrazolium (NBT) test is negative. The underlying defect is in which enzyme system?

• A NADPH oxidase ✓
• B Bruton tyrosine kinase (BTK)
• C Adenosine deaminase (ADA)
• D CD40 ligand

Explanation

This describes chronic granulomatous disease (CGD), where a defective NADPH oxidase system prevents phagocytes from generating reactive oxygen species to kill catalase-positive organisms. The negative NBT test confirms defective oxidative burst. BTK mutations cause XLA. ADA deficiency causes SCID. CD40 ligand defects cause hyper-IgM syndrome.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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