A newborn is found to have absent thymus and parathyroid glands with a conotruncal cardiac defect (truncus arteriosus) and a characteristic facial dysmorphism. Absence of migration of neural crest cells from which region is responsible?

• A Cranial neural crest from rhombomeres 1–2, populating the first pharyngeal arch
• B Cardiac neural crest (postotic rhombomeres 6–8), which migrates into pharyngeal arches 3, 4, and 6 ✓
• C Trunk neural crest giving rise to adrenal chromaffin cells
• D Vagal neural crest giving rise to enteric nervous system

Explanation

DiGeorge sequence (22q11.2 deletion) results from failure of cardiac neural crest cells (from postotic rhombomeres 6–8) to migrate into the 3rd, 4th, and 6th pharyngeal arches. These cells are required for septation of the truncus arteriosus, formation of the thymus (3rd pouch) and inferior parathyroids (3rd pouch), and superior parathyroids (4th pouch). Cranial neural crest forms craniofacial skeletal elements. Trunk neural crest contributes to adrenal medulla and dorsal root ganglia. Vagal neural crest forms the enteric nervous system.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.