A 3-year-old boy has recurrent otitis media and pneumonia with marked neutrophilic leukocytosis but no pus at infected sites. His neutrophils show normal integrin expression and normal oxidative burst. Blood grouping reveals the rare Bombay phenotype. The underlying defect is:

• A Mutation in ITGB2 encoding the beta-2 integrin chain
• B Impaired GDP-fucose transport preventing synthesis of sialylated Lewis X ligands ✓
• C Defective lysosomal trafficking protein LYST
• D NADPH oxidase subunit mutation abolishing superoxide generation

Explanation

This boy has leukocyte adhesion deficiency type II: mutations in the GDP-fucose transporter (SLC35B1) prevent fucosylation of glycans, so neutrophils cannot express sialyl-Lewis X, the ligand for endothelial selectins. Rolling fails, and the Bombay blood phenotype results from absence of the same fucosylated H antigen on red cells. ITGB2 mutation defines LAD-I, LYST defines Chediak-Higashi, and NADPH oxidase defects define chronic granulomatous disease, all excluded here by normal findings.

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.