A 4-year-old girl has recurrent severe candidiasis, persistent viral infections, and hypocalcemic tetany since infancy. Chest radiograph shows absence of the thymic shadow, and echocardiography reveals truncus arteriosus. Serum calcium is 7.0 mg/dL. Which chromosomal abnormality should be suspected?
- A Trisomy of chromosome 21
- B Deletion on chromosome 22q11.2 ✓
- C Deletion on chromosome 15q11-q13
- D Monosomy of the X chromosome
Correct answer: B. Deletion on chromosome 22q11.2
Explanation
DiGeorge syndrome results from a microdeletion at 22q11.2 causing failed development of the third and fourth pharyngeal pouches. This produces thymic aplasia with defective T-cell maturation, parathyroid hypoplasia causing hypocalcemia, and conotruncal cardiac anomalies such as truncus arteriosus and tetralogy of Fallot. Trisomy 21 causes Down syndrome, deletion 15q11-q13 causes Prader-Willi or Angelman syndromes, and monosomy X causes Turner syndrome, none of which combine thymic aplasia with hypocalcemia and conotruncal defects.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.