Answer:
Treacher Collins syndrome (TCS) or mandibulofacial dysotosis is an autosomal dominant condition with variable expressivity. It is characterized by bilaterally symmetric abnormalities of structures derived from the first and second branchial arches. The adult patient with fully expressed Treacher Collins syndrome has a convex facial profile with a prominent nasal dorsum above a retrusive lower jaw and chin. The eyes are characterized by an antimongoloid slant, hypoplastic lower eyelids with colobomata, absence of medial eyelid cilia, and inferior-lateral orbital dystopia. Long “tongue-shaped” sideburns extend into the preauricular region. The external ears are absent, malformed, or malposed, and hearing is impaired as a result of variable degrees of aural atresia. Cleft palate, with or without cleft lip, and choanal atresia are present variably. The most characteristic skeletal finding is hypoplasia of the malar bones, often with clefting through the arches. The maxillary and mandibular bones are also characteristically hypoplastic with antigonial notching of the angle of the mandible and variable effects on the temporomandibular joints. There is angle class II anterior open-bite malocclusion, a steep (clockwise rotated) occlusal plane.Craniosynostosis is not a feature of TCS, but the neurocranium will have an abnormal shape (decreased anterior-posterior length and diminished bitemporal width) that is evident during childhood and remains through adulthood. The degree of malformation present at birth is relatively stable and nonprogressive.