A 4-year-old boy has recurrent abscesses caused by Staphylococcus aureus, Serratia marcescens, and Aspergillus, along with granulomatous lymphadenitis and hepatosplenomegaly. The dihydroxyrhodamine (flow cytometry oxidative burst) test shows no respiratory burst in his neutrophils. His maternal uncle died of a similar illness. The defective protein is:

• A gp91phox (CYBB), the membrane component of NADPH oxidase ✓
• B Bruton tyrosine kinase (BTK)
• C STAT3, causing impaired Th17 differentiation
• D Wiskott-Aldrich syndrome protein (WASP)

Explanation

Chronic granulomatous disease results from defective phagocyte NADPH oxidase, so superoxide cannot be generated and catalase-positive organisms survive inside neutrophils. About two thirds of cases are X-linked from CYBB mutations encoding gp91phox, matching the affected male relatives here. STAT3 defects cause autosomal dominant hyper-IgE syndrome with staphylococcal abscesses but a normal oxidative burst, and BTK and WASP are B-cell and cytoskeletal defects respectively, unrelated to respiratory burst.

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.