DiGeorge syndrome results from a microdeletion at chromosome 22q11.2. The primary immunologic consequence is:

• A Complete absence of both B and T lymphocytes due to defective cytokine receptor signaling
• B Absent thymic development causing T-cell lymphopenia with preserved B-cell numbers and hypergammaglobulinemia ✓
• C Selective IgA deficiency due to absent class-switch recombination in Peyer's patches
• D Neutrophil killing defect due to absent NADPH oxidase complex

Explanation

The 22q11.2 deletion impairs development of the 3rd and 4th pharyngeal pouches, resulting in thymic aplasia or hypoplasia. Without the thymic microenvironment, T-cell maturation is severely deficient (T-cell lymphopenia). B cells develop normally in the bone marrow but, lacking T-cell help, cannot mount effective T-dependent antibody responses; however, initial immunoglobulin levels may be near-normal or even elevated non-specifically. The clinical triad is conotruncal cardiac defects, hypocalcemia (absent parathyroids), and T-cell immunodeficiency. SCID (absent B and T) results from defects in common γ-chain, ADA, or RAG genes. Chronic granulomatous disease involves the NADPH oxidase.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.