A 6-year-old boy is evaluated for recurrent bacterial infections since infancy. Flow cytometry shows absent B cells but normal T cells and NK cells. Serum immunoglobulins are markedly reduced. BTK gene mutation is confirmed. Which of the following best describes the immunological mechanism?
- A Arrest of B-cell maturation at the pro-B to pre-B transition due to absent Bruton tyrosine kinase ✓
- B Defective VDJ recombination affecting all lymphocytes
- C Absence of thymic education causing combined immunodeficiency
- D Defective class-switch recombination from IgM to IgG
Correct answer: A. Arrest of B-cell maturation at the pro-B to pre-B transition due to absent Bruton tyrosine kinase
Explanation
X-linked agammaglobulinemia (XLA) results from BTK mutations that arrest B-cell development at the pro-B to pre-B transition; mature B cells, plasma cells, and all immunoglobulin classes are absent. VDJ recombination is not the primary defect; T cells are normal, ruling out combined immunodeficiency; class-switch defects cause Hyper-IgM syndrome where IgM is elevated and mature B cells are present.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.