| Locus (OMIM) | Gene (OMIM) | Inheritance | Key Locus References (PubMed) | Key Gene References (PubMed) | Evidence (ClinGen)  |
|---|---|---|---|---|---|
| TCS1 | TCOF1 | Autosomal Dominant | Balestrazzi et al., 1983; Jabs et al., 1991; Dixon et al., 1992; Dixon et al., 1993 | Treacher Collins Syndrome Collaborative Group, 1996 | Definitive |
| TCS2 | POLR1D | Autosomal Dominant | Dauwerse et al., 2011 | Dauwerse et al., 2011 | not reviewed |
| TCS2 | POLR1D | Autosomal Recessive | Schaefer et al., 2014 | Schaefer et al., 2014 | not reviewed |
| TCS3 | POLR1C | Autosomal Recessive | Dauwerse et al., 2011 | Dauwerse et al., 2011 | Moderate |
| TCS4 | POLR1B | Autosomal Dominant | Sanchez et al., 2020 | Sanchez et al., 2020 | not reviewed |
Treacher Collins syndrome is characterized by coloboma of the lower eyelid (the upper eyelid is involved in Goldenhar syndrome), micrognathia, microtia, hypoplasia of the zygomatic arches, macrostomia, and inferior displacement of the lateral canthi with respect to the medial canthi. The disease-causing gene, TCOF1, encodes a protein of 1,411 amino acids (TREACLE) with a structure that is shared with nucleolar trafficking proteins in other species, suggesting that TCOF1 plays a role in nucleolar-cytoplasmic transport. The detection rate for mutations in this gene in persons with the TCOF1 phenotype is approximately 60%, and in nearly all cases, the result is the introduction of a premature stop codon into the predicted protein (Edwards et al., 1997).