An abnormality of vibrational conductance of sound to the inner ear leading to impairment of sensory perception of sound.

Underdevelopment of the external ear.

Developmental hypoplasia of the mandible.

Underdevelopment of the malar prominence of the jugal bone (zygomatic bone in mammals), appreciated in profile, frontal view, and/or by palpation.

Underdevelopment of the zygomatic bone. That is, a reduction in size of the zygomatic bone, including the zygomatic process of the temporal bone of the skull, which forms part of the zygomatic arch.

Treacher Collins syndrome is a disorder of craniofacial development. The features include downslanting palpebral fissures, coloboma of the eyelid, micrognathia, microtia and other deformity of the ears, hypoplastic zygomatic arches, and macrostomia. Conductive hearing loss and cleft palate are often present (Dixon, 1996). Genetic Heterogeneity of Treacher Collins Syndrome Treacher Collins syndrome-2 (TCS2; 613717) is caused by mutation in the POLR1D gene (613715) on chromosome 13q12. Treacher Collins syndrome-3 (TCS3; 248390) is caused by mutation in the POLR1C gene (610060) on chromosome 6p21. Treacher Collins syndrome-4 (TCS4; 618939) is caused by mutation in the POLR1B gene (602000) on chromosome 2q14.

The palpebral fissure inclination is more than two standard deviations below the mean.

A short discontinuity of the margin of the lower eyelid.

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).