A newborn has delayed separation of the umbilical cord at 4 weeks, recurrent bacterial infections without pus formation, and persistent neutrophilia of 30,000/mm3 even between infections. Flow cytometry shows absence of CD11b expression on neutrophils. The underlying genetic defect involves:
- A ITGB2 encoding the beta-2 integrin chain shared by LFA-1, Mac-1, and p150,95 ✓
- B ITGAM encoding the alpha chain of Mac-1
- C ELANE encoding neutrophil elastase causing defective nuclear segmentation
- D CXCR4 mutation causing retention of mature neutrophils in the marrow
Correct answer: A. ITGB2 encoding the beta-2 integrin chain shared by LFA-1, Mac-1, and p150,95
Explanation
Leukocyte adhesion deficiency type 1 results from ITGB2 mutations abolishing the beta-2 integrin subunit (CD18) common to LFA-1, Mac-1, and p150,95, preventing firm adhesion and transmigration of neutrophils through endothelium. Hence no pus, delayed cord separation, and marked neutrophilia. ELANE mutations cause cyclic or congenital neutropenia with low counts, which contradicts the persistent neutrophilia here.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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