Hypomandibular faciocranial dysostosis is a cranial malformation characterized by facial dysmorphism (proptosis, frontal bossing, midface and zygomatic arches hypoplasia, short nose with anteverted nostrils, microstomia with persistent buccopharyngeal membrane, severe hypoglossia with glossoptosis, severe mandibular hypoplasia, and low set ears) associated with laryngeal hypoplasia and craniosynostosis. Other variable features include cleft palate, optic nerve coloboma and choanal stenosis.

Cleft palate is a developmental defect of the palate resulting from a failure of fusion of the palatine processes and manifesting as a separation of the roof of the mouth (soft and hard palate).