Treacher Collins syndrome

Treacher Collins syndrome, also known as mandibulofacial dysostosis, is an autosomal dominant genetic abnormality and results from bilateral malformations of 1^st and 2^nd branchial arches. 

Epidemiology

The incidence is estimated at approximately 1 in 50,000 live births, with 60% of cases being sporadic, and 40% having a family history of the condition ¹. 

Clinical manifestations

Abnormalities in the structures derived from the first and second pharyngeal pouch, groove, and arch.

Pathology

The majority of cases (80-90%) are due to mutations of the TCOF1 gene, located on chromosome 5, which encodes a nucleolar phosphoprotein “Treacle” ¹. Two other genes also are known to cause Treacher Collins syndrome (POLR1C and POLR1D) ³. 

Radiographic features

• dental and mandibular 
  • retrognathia
  • micrognathia
  • macrostomia
  • hypoplasia or aplasia of the condylar and coronoid processes of the mandible
  • marked bowing of the lower border of the mandible
  • concave curvature of the horizontal ramus of the mandible is pathognomonic
  • may be associated with cleft palate and absence of parotid glands

• zygomatic arch: malformed, underdeveloped or absent
• otic
  • microtia and aplasia of the external auditory meatus
  • conductive hearing defects are present
• nasal
  • obliteration of the nasofrontal angle with narrow nares
  • hypoplasia of the alar cartilages
  • hypoplastic paranasal sinuses
• ocular
  • downward slanting palpebral fissures, due to lack of support from zygoma
  • absent eyelids of the lower inner third of the eye
  • notched iris
  • notched choroid and colobomas

EtymologyHistory and etymology

Treacher Collins syndrome was named after Edward Treacher Collins (1862-1932 ), an English ophthalmologist and surgeon who published two cases in 1900, describing many of the features ^1,4. The condition is believed, however, to have been described first by Thompson in 1846 ⁴. In 1949 Franceschetti and Klein published the first comprehensive review of the topic and introduced the term Mandibulofacial dysostosis ^1,4.