In DiGeorge syndrome, thymic aplasia results in profound deficiency of which immune cell type, and what is the chromosome involved?

• A T-lymphocytes; chromosome 22q11.2 deletion ✓
• B B-lymphocytes; chromosome 14q deletion
• C NK cells; chromosome 6p21 deletion
• D Dendritic cells; chromosome 17p13 deletion

Explanation

DiGeorge syndrome results from a microdeletion at chromosome 22q11.2, disrupting development of the 3rd and 4th pharyngeal pouches. The thymus (derived from 3rd pharyngeal pouch) fails to develop, leading to absent or severely reduced T-cell production while B-cell counts are normal. This selective T-cell deficiency causes susceptibility to intracellular organisms, fungi, and viruses. Associated features include hypocalcaemia (absent parathyroids from 4th pouch), conotruncal cardiac defects, and characteristic facies — the CATCH-22 mnemonic.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.