DiGeorge syndrome results from a 22q11.2 deletion affecting pharyngeal pouch development. The immune defect is best characterized as:
- A T-cell lymphopenia due to thymic aplasia/hypoplasia with preserved B cells and Ig levels ✓
- B Combined T- and B-cell deficiency with absent adenosine deaminase (ADA)
- C B-cell deficiency with absent Bruton tyrosine kinase (BTK)
- D NK cell deficiency with absent MHC class I surface expression
Correct answer: A. T-cell lymphopenia due to thymic aplasia/hypoplasia with preserved B cells and Ig levels
Explanation
DiGeorge syndrome (22q11.2 deletion / velocardiofacial syndrome) involves failure of the 3rd and 4th pharyngeal pouches to develop, causing aplasia/hypoplasia of the thymus and parathyroid glands. Without thymic education, T-cell maturation is severely impaired (T-cell lymphopenia), while B-cell numbers and immunoglobulin levels are initially normal (though antibody production is impaired over time due to T-cell help deficiency). ADA-SCID causes combined T+B+NK deficiency. XLA (BTK mutation) causes B-cell deficiency.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.