DiGeorge syndrome results from a microdeletion at chromosome 22q11.2 causing failure of development of the third and fourth pharyngeal pouches. The primary immunological consequence is:

• A Thymic aplasia/hypoplasia causing T-cell deficiency ✓
• B Absence of B lymphocytes with agammaglobulinemia
• C Absent complement C3 causing recurrent encapsulated bacterial infections
• D Defective phagocyte respiratory burst (chronic granulomatous disease)

Explanation

The third and fourth pharyngeal pouches give rise to the thymus and inferior parathyroids. In DiGeorge syndrome (22q11.2 deletion), thymic aplasia causes profound T-cell deficiency while B-cell numbers are normal (though functional antibody responses are impaired due to lack of T-cell help). The classic triad is congenital heart defects, hypocalcemia (hypoparathyroidism), and T-cell immunodeficiency.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.