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
Mandibulofacial dystosis, also known as Treacher Collins syndrome, is an autosomal dominant disorder affecting neural crest migration into the first pharyngeal arch. The first pharyngeal arch is innervated by cranial nerve V (specifically V2 and V3) and is responsible for forming the maxilla, mandible, middle ear, and muscles of mastication.
Answer choice B: Fourth, is incorrect. The fourth branchial arch is innervated by cranial nerve X (vagus) and the superior laryngeal nerve and is responsible for forming laryngeal cartilage (thyroid, epiglottic) and pharyngeal constrictors.
Answer choice C: Second, is incorrect. The second branchial arch is innervated by cranial nerve VII (facial) and is responsible for forming the muscles of facial expression, the stapes, and the upper hyoid.
Answer choice D: Sixth, is incorrect. The sixth branchial arch is innervated by cranial nerve X (vagus) and the recurrent laryngeal nerve and is responsible for forming the laryngeal cartilage (cricoid, arytenoid, corniculate, and cuneiform) and the intrinsic laryngeal muscles.
Answer choice E: Third, is incorrect. The third branchial arch is innervated by cranial nerve IX (glossopharyngeal) and is responsible for forming the lower hyoid and stylopharyngeus muscle.
Key Learning Point
In embryologic development, the first pharyngeal arch is innervated by cranial nerve V and is responsible for forming the maxilla, mandible, middle ear, and muscles of mastication.
