A newborn develops tetanic spasms and carpopedal spasm on day 3 of life. Echocardiography shows truncus arteriosus, and chest imaging shows absence of the thymic shadow. Serum calcium is 6.8 mg/dL. Which chromosomal abnormality should be suspected?

• A Deletion of 22q11.2 ✓
• B Mutation in the WAS gene on the X chromosome
• C Deletion of 17p13.1
• D Trisomy of chromosome 21

Explanation

DiGeorge syndrome results from failure of third and fourth pharyngeal pouch development due to a microdeletion at 22q11.2, causing thymic aplasia with T cell deficiency, parathyroid hypoplasia with neonatal hypocalcemic tetany, and conotruncal cardiac defects such as truncus arteriosus. Williams syndrome involves elastin deletion at 7q11, not 17p13, which is the locus deleted in Miller-Dieker lissencephaly.

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.