A patient with chronic granulomatous disease (CGD) fails to kill ingested Staphylococcus aureus. The fundamental defect is absence of functional:

• A Myeloperoxidase, preventing hypochlorous acid generation
• B Defensins in azurophilic granules
• C NADPH oxidase (phox complex), preventing respiratory burst superoxide generation ✓
• D Lysosomal cathepsins in secondary granules

Explanation

Chronic granulomatous disease results from mutations in NADPH oxidase subunits (most commonly CYBB encoding gp91phox, X-linked; less commonly p47phox, p67phox — autosomal recessive). Without the oxidative burst, superoxide and downstream ROS (H2O2, HOCl via MPO) are not generated, impairing killing of catalase-positive organisms (Staphylococcus, Aspergillus, Serratia, Nocardia, Burkholderia). The NBT (nitroblue tetrazolium) test is negative. Myeloperoxidase deficiency is typically milder. Defensins and cathepsins are intact in CGD.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.