In DiGeorge syndrome (22q11.2 deletion), the primary immunological defect is:

• A Absent B cells due to failure of immunoglobulin heavy chain rearrangement
• B Deficient T cells due to thymic aplasia with intact humoral immunity ✓
• C Combined T and B cell deficiency due to gamma-chain mutation
• D Neutrophil killing defect due to NADPH oxidase deficiency

Explanation

DiGeorge syndrome results from 22q11.2 deletion affecting pharyngeal pouch development, leading to thymic hypoplasia or aplasia. The primary defect is reduced or absent T lymphocyte maturation, causing defective cell-mediated immunity. B cell numbers are normal but T cell-dependent antibody responses (particularly IgG) are impaired. X-linked agammaglobulinemia affects B cells. SCID involves gamma-chain deficiency. CGD is the NADPH oxidase defect.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.