A newborn presents with conotruncal heart defect (persistent truncus arteriosus), absent thymus, hypocalcaemia, and abnormal facial features. Failure of migration of neural crest cells from which rhombomeric level primarily accounts for the cardiovascular defect?

• A Rhombomere 1–2
• B Rhombomere 3–4
• C Prosencephalic neural crest
• D Rhombomere 6–8 (vagal neural crest) ✓

Explanation

DiGeorge syndrome (22q11.2 deletion; TBX1 gene) involves defective migration of cardiac neural crest cells from rhombomeres 6–8 (the vagal crest). These cells populate the outflow tract septum (aorticopulmonary septum) and pharyngeal arch mesenchyme. Failure produces conotruncal defects, absent parathyroids (hypocalcaemia), absent thymus, and dysmorphic facial features. Rhombomeres 1–2 give rise to sensory ganglia of CN V/VII; rhombomeres 3–4 cells migrate to the second pharyngeal arch.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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