A patient with DiGeorge syndrome (22q11.2 deletion) lacks thymic tissue. The primary immunological defect expected is:

• A Absent B-cell production with absent immunoglobulins but normal T-cell function
• B Combined T and B cell aplasia with absent NK cells and bare lymphocyte syndrome
• C Normal T and B cells but absent granulocytes and monocytes causing bacterial susceptibility
• D Absent T-cell maturation with preserved B-cell numbers but progressive loss of T-cell-dependent antibody responses ✓

Explanation

DiGeorge syndrome results from failure of development of the 3rd and 4th pharyngeal pouches (thymic and parathyroid aplasia). Thymic aplasia prevents T-cell education and maturation; T cells fail to undergo positive and negative selection. Patients have absent or severely reduced T cells (particularly CD4+ and CD8+ cells), while B-cell production from bone marrow is unaffected (B-cell numbers may be normal or even elevated). However, without T-cell help, B cells cannot mount T-dependent (class-switched) antibody responses. The clinical triad is: conotruncal cardiac defects, hypoparathyroidism (hypocalcaemia), and T-cell immunodeficiency. Severe combined immunodeficiency (SCID) involves both T and B cell absence; X-linked agammaglobulinaemia involves B-cell absence with normal T cells.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.