Step 1

Embryology 1

A two-week-old boy presents to the craniofacial clinic for evaluation facial abnormalities. After evaluation by a geneticist, he is diagnosed with mandibulofacial dystosis (Treacher Collins syndrome), an autosomal dominant disease in which patients present with hypoplasia of zygomatic bones, hypoplasia of mandible, conductive hearing loss, and normal intelligence.

This syndrome is due to a gene mutation affecting neural crest cell migration into which pharyngeal arch?

  • A) First
  • B) Fourth
  • C) Second
  • D) Sixth
  • E) Third


Leora Aizman


Dr. Ted O'Connell