A 4-year-old boy has recurrent abscesses due to Staphylococcus aureus and Aspergillus since infancy. The nitroblue tetrazolium test shows no dye reduction by his neutrophils. The defective enzyme normally catalyses which reaction?

• A Transfer of electrons from NADPH to oxygen, generating superoxide ✓
• B Conversion of chloride ion to hypochlorous acid using H2O2
• C Disproportionation of superoxide anion to hydrogen peroxide
• D Reduction of hydrogen peroxide to water using glutathione

Explanation

This is chronic granulomatous disease caused by defects in the phagocyte NADPH oxidase complex (gp91phox, p47phox subunits among others). The enzyme transfers electrons from NADPH to molecular oxygen, producing the superoxide radical that initiates the respiratory burst. Option B describes myeloperoxidase, whose deficiency still allows a positive NBT test because superoxide generation is intact, which is exactly what kills that distractor here.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.