There are many and varied forms of mandibulofacial dysostosis (Treacher Collins syndrome), which is inherited in an autosomal dominant manner. The structures most affected derive from the first pharyngeal arch. Symptoms are abnormal development of the outer and inner ear (conductive hearing loss), hypoplasia of facial bones (zygomatic bone, mandibula and palate).
The Robin Sequence also affects the derivatives of the first pharyngeal arch. The lower jaw does not grow sufficiently (micrognathia), which causes the tongue to remain between the palatal processes. As a result, fusion of the palatine processes is impeded. The Robin Sequence often occurs in combination with other congenital anomalies of the mandibula.
Pharyngeal diverticulum often appears at the transition from the pharynx to the oesophagus. In this condition, the pharyngeal mucosa evaginates in a dorsal direction due to a weakness of the muscular wall of the pharynx. A neuromuscular dysfunction is thought to be a prime reason for the formation of this diverticulum.