Treacher-Collins syndrome results from reduced neural crest cell migration to which arches?

• A. First arch only
• B. Second arch only
• C. First and second arches
• D. All arches

Answer: (C)

Treacher-Collins syndrome arises when neural crest cells fail to populate the first two pharyngeal (branchial) arches. These arches contribute most of the midface and ear region: the first arch forms the maxilla, mandible, and much of the cheek area, while the second arch contributes structures of the ear and parts of the hyoid. When migration into these arches is reduced, the midface and ear regions underdevelop, leading to the characteristic facial features of the syndrome, such as malar hypoplasia and ear anomalies. This explains why the problem is localized to the front of the face rather than involving all arches.