A newborn presents with absent thymus and parathyroid glands, conotruncal cardiac defect, and hypocalcemia. The embryological structure most responsible for this syndrome is:
- A Neural crest cells migrating into pharyngeal arches 3 and 4 ✓
- B Endoderm of the first pharyngeal pouch
- C Mesoderm of the second pharyngeal arch
- D Paraxial mesoderm of somites 1–4
Explanation
DiGeorge syndrome (22q11.2 deletion) results from failure of neural crest cell migration into the 3rd and 4th pharyngeal arches and pouches. Neural crest cells are required for formation of the thymus (3rd pouch), inferior parathyroids (3rd pouch), superior parathyroids (4th pouch), and for septation of the cardiac outflow tract (conotruncal defects like truncus arteriosus, interrupted aortic arch, ToF). Absent parathyroids cause neonatal hypocalcemia, absent thymus causes T-cell immunodeficiency. The 1st pharyngeal pouch forms the Eustachian tube and middle ear. The 2nd arch mesoderm forms facial muscles.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.