A 30-year-old woman has had recurrent episodes of oral and vaginal candidiasis since adolescence. Bacterial infections have been unremarkable. Neutrophil studies show completely normal chemotaxis, normal phagocytosis, and a normal oxidative burst on the dihydrorhodamine assay. Which intracellular defect best explains these findings?

• A Defective NADPH oxidase generating no superoxide radical
• B Defective lysosomal trafficking due to LYST mutation
• C Absence of CD18 preventing beta-2 integrin expression
• D Myeloperoxidase deficiency preventing hypochlorous acid formation ✓

Explanation

Myeloperoxidase converts hydrogen peroxide and chloride into hypochlorous acid, the main microbicidal oxidant within phagolysosomes; its loss selectively impairs killing, especially of Candida albicans, while phagocytosis and the respiratory burst remain normal, matching the normal dihydrorhodamine test here. NADPH oxidase failure defines chronic granulomatous disease with a positive family history and catalase-positive organisms, CD18 absence defines LAD, and LYST mutation defines Chediak-Higashi syndrome.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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