A 9-year-old girl has recurrent mucocutaneous infections with Candida albicans and Staphylococcus aureus. Neutrophil chemotaxis, phagocytosis, and oxidative burst testing are all normal, and the nitroblue tetrazolium dye reduction test is positive. Electron microscopy of neutrophils shows failure of intracellular microbial killing despite normal oxygen radical generation. The most likely defect is:

• A Deficiency of NADPH oxidase
• B Myeloperoxidase deficiency ✓
• C Defect in the beta-2 integrin chain (CD18)
• D Defective lysosomal trafficking (LYST gene mutation)

Explanation

Myeloperoxidase deficiency impairs conversion of hydrogen peroxide to hypochlorite (HOCl), the major microbicidal oxidant, yet the NADPH oxidase oxidative burst itself remains intact, so the NBT test is positive. This distinguishes it from chronic granulomatous disease, where oxidase deficiency makes the NBT test negative. Chemotaxis and phagocytosis are normal, excluding LAD, and giant lysosomal granules characteristic of Chediak-Higashi syndrome are absent.

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.