Treacher Collins syndrome

Treacher Collins syndrome (TCS) is an autosomal dominant congenital disorder characterized by craniofacial deformities, involving ears, eyes and cheekbones and goes along with normal intelligence.^[3]:577 It is caused by a mutation in the TCOF1 gene most commonly, or of POLR1C or POLR1D. The typical physical features include downward-slanting eyes, micrognathia (a small lower jaw), conductive hearing loss, underdeveloped zygoma, drooping part of the lateral lower eyelids, and malformed or absent ears.

TCS occurs in about one in 50,000 births in Europe.^[4] The syndrome is named after Edward Treacher Collins (1862–1932), the English surgeon and ophthalmologist who described its essential traits in 1900.^[5][6]

Signs and symptoms

Symptoms in people with Treacher Collins syndrome vary. Some individuals may be so mildly affected that they remain undiagnosed; others can have severe facial involvement and life-threatening airway compromise.^[7] Most of the features of TCS are bilateral and are already recognisable at birth.

Affected persons are mostly characterized by these abnormalities:

• Hypoplasia of the facial bones: Most described is an underdeveloped mandibular and zygomatic bone. This leads to a small and malformed jaw. Mandible hypoplasia can result in a malocclusion.^[8]
• Ear anomalies: The external ear anomalies consist of small, rotated, or even absent auricles. Also symmetric, bilateral stenosis or atresia of the external auditory canals is described.^[9] In most cases, the ossicles and the middle ear cavity were dysmorphic. Inner ear malformations are rarely described. As a result of these abnormalities, a majority of the individuals with TCS have conductive hearing loss.^[10]
• Most affected persons experience eye problems, varying from colobomata of the lower eyelids and aplasia of lid lashes to short, down-slanting palpebral fissures, and missing eyelashes. Vision loss can occur and is associated with strabismus, refractive errors, and anisometropia.^[9][11]
• Cleft palate ^[8]
• Airway problems, which are often a result of mandibular hypoplasia, can occur.^[8]

An abnormally shaped skull is not distinctive for Treacher Collins syndrome, but brachycephaly with bitemporal narrowing is sometimes observed.^[9]

Dental anomalies are seen in 60%, consisting of tooth agenesis (33%), enamel disformaties (20%), and malplacement of the maxillary first molars (13%). In some cases, dental anomalies in combination with mandible hypoplasia result in a malocclusion. This can lead to problems with food intake and the ability to close the mouth.

Features related to TCS that are seen less frequently include^[8]

• Nasal deformity
• High-arched palate
• Coloboma of the upper lid ^[12]
• Ocular hypertelorism ^[12]
• Choanal atresia
• Macrostomia
• Preauricular hair displacement

The general public may associate facial deformity with developmental delay, and lower intelligence, but intelligence of persons with TCS is usually normal. The psychological and social problems associated with facial deformity can affect quality of life in people with TCS.

Causes

TCS occurs in about one in 50,000 births in Europe.^[4] Mutations in TCOF1, POLR1C, or POLR1D genes can cause Treacher Collins syndrome.^[13] TCOF1 gene mutations are the most common cause of the disorder, accounting for 81 to 93% of all cases. POLR1C and POLR1D gene mutations cause an additional 2% of cases. In individuals without an identified mutation in one of these genes, the genetic cause of the condition is unknown. The TCOF1, POLR1C, and POLR1D genes code for proteins which play important roles in the early development of bones and other tissues of the face. Mutations in these genes reduce the production of rRNA, which may trigger the self-destruction (apoptosis) of certain cells involved in the development of facial bones and tissues. It is unclear why the effects of a reduction in rRNA are limited to facial development.

Genetic mutation

TCOF1 is the only gene currently known to be associated with TCS, a mutation in this gene being found in 90-95% of the individuals with TCS.^[8][14] However, in some individuals with typical symptoms of TCS, mutations in TCOF1 have not been found.^[15] Investigation of the DNA has resulted in the identification of the kind of mutations found in TCOF1. The majority of mutations are small deletions or insertions, though splice site and missense mutations also have been identified.^{[8][16][17][18]} Mutation analysis has unveiled more than 100 disease-causing mutations in TCOF1, which are mostly family-specific mutations. The only recurrent mutation accounts for about 17% of the cases.^[19]

Treacher Collins syndrome is inherited in an autosomal-dominant pattern.

Function of the TCOF1 gene

TCOF1 codes for a relatively simple, nucleolar protein called treacle.^[14] Mutations in TCOF1 lead to haploinsufficiency of the treacle protein.^[20] Haploinsufficiency occurs when a diploid organism has only one functional copy of a gene, because the other copy is inactivated by a mutation. Thereby, the other functional gene does not produce enough of a gene-product to have the expected function, resulting in an abnormal/ disease state. Haploinsufficiency of the treacle protein leads to a depletion of the neural crest cell precursor, which leads to a reduced number of crest cells migrating to the first and second pharyngeal arches. These crest cells play an important role in the development of the craniofacial appearance.^[16][21] So down regulation of treacle expression results in craniofacial defects and growth retardation.

Genetic counselling

TCS is inherited in an autosomal dominant manner and the penetrance of the affected gene is almost complete.^[22] Some recent investigations, though, described some rare cases in which the penetrance in TCS was not complete. Causes may be a variable expressivity, an incomplete penetrance ^[23] or germline mosaicism.^[24] Only 40% of the mutations are inherited. The remaining 60% are a result of a de novo mutation.^[25] In the outcome of the disease, inter- and intrafamilial variability occurs. This suggests, when an affected child is born, it is important to investigate the parents to determine whether the affected gene is present. A parent could have a mild and undiagnosed TCS. In this case, the risk of having another affected child is 50%. If the parents do not have the affected gene, the recurrence risk appears to be low.^[22] In following generations, the severity of the clinical symptoms increases.^[17]

Diagnosis

The diagnosis of Treacher Collins syndrome relies upon clinical and radiographic findings.

Clinical findings

A set of typical symptoms occurs within Treacher Collins syndrome, which can be detected by a critical clinical view. The wide spectrum of diseases which have similar characteristics make it sometimes difficult to diagnose TCS.^[26] The OMENS classification was developed as a comprehensive and stage-based approach to differentiate the diseases. This acronym describes five distinct dysmorphic manifestations, namely orbital asymmetry, mandibular hypoplasia, auricular deformity, nerve development, and soft-tissue disease. The table below shows the OMENS classification in more detail.^[27]

Orbit

• O0: normal orbital size, position
• O1: abnormal orbital size
• O2: abnormal orbital position
• O3: abnormal orbital size and position

Mandible

• M0: normal mandible
• M1: small mandible and glenoid fossa with short ramus
• M2: ramus short and abnormally shaped

1. 2A: glenoid fossa in anatomical acceptable position
2. 2B: Temperomandibular joint inferiorly (TMJ), medially, anteriorly displaced, with severely hypoplastic condyle

• M3: Complete absence of ramus, glenoid fossa, and TMJ

Ear

• E0: normal ear
• E1: Minor hypoplasia and cupping with all structures present
• E2: Absence of external auditory cannel with variable hypoplasia of the auricle
• E3: Malposition of the lobule with absent auricle, lobular remnant usually inferior anteriorly displaced

Facial nerve

• N0: No facial nerve involvement
• N1: Upper facial nerve involvement (temporal or zygomatic branches)
• N2: Lower facial nerve involvement (buccal, mandibular or cervical)
• N3: All branches affected

Soft tissue

• S0: No soft tissue or muscle deficiency
• S1: Minimal tissue or muscle deficiency
• S2: Moderate tissue or muscle deficiency
• S3: Severe tissue or muscle deficiency

Radiological findings

Radiologic manifestations can be used to confirm the diagnosis. Imaging evaluation consists of X-rays (radiographs), CT scans, MRI, and/or ultrasound.

Radiographs

A few techniques are used to confirm the diagnosis in TCS. An orthopantomogram (OPG) is a panoramic dental X-ray of the upper and lower jaw. It shows a two-dimensional image from ear to ear. Particularly, OPG facilitates an accurate postoperative follow-up and monitoring of bone growth under a mono- or double-distractor treatment. Thereby, some TCS features could be seen on OPG, but better techniques are used to include the whole spectrum of TCS abnormalities instead of showing only the jaw abnormalities.^[26] Another method of radiographic evaluation is taking an X-ray image of the whole head. The lateral cephalometric radiograph in TCS shows hypoplasia of the facial bones, like the malar bone, mandible, and the mastoid.^[26] Finally, occipitomental radiographs are used to detect hypoplasia or discontinuity of the zygomatic arch.^[28]

CT scan

A temporal-bone CT using thin slices makes it possible to diagnose the degree of stenosis and atresia of the external auditory channel, the status of the middle ear cavity, the absent or dysplastic and rudimentary ossicles, or the inner ear abnormalities such as a deficient cochlea. Two- and three-dimensional CT reconstructions with VRT and bone and skin-surfacing are helpful for more accurate staging and the three-dimensional planning of mandibular and external ear reconstructive surgery.

Differential diagnosis

Other diseases have similar characteristics to Treacher Collins syndrome. In the differential diagnosis, one should consider the acrofacial dysostoses. The facial appearance resembles that of Treacher Collins syndrome, but additional limb abnormalities occur in those persons. Examples of these diseases are Nager syndrome and Miller syndrome. The oculoauriculovertebral spectrum should also be considered in the differential diagnosis. An example is hemifacial microsomia, which primarily affects development of the ear, mouth, and mandible. This anomaly may occur bilaterally. Another disease which belongs to this spectrum is Goldenhar syndrome, which includes vertebral abnormalities, epibulbar dermoids and facial deformities.^[29]

Treatment

The treatment of individuals with TCS may involve the intervention of professionals from multiple disciplines. The primary concerns are breathing and feeding, as a consequence of the hypoplasia of the mandibula and the obstruction of the hypopharynx by the tongue. Sometimes, they may require a tracheostomy to maintain an adequate airway,^[30] and a gastrostomy to assure an adequate caloric intake while protecting the airway. Corrective surgery of the face is performed at defined ages, depending on the developmental state.^[31]

An overview of the present guidelines:

• If a cleft palate is present, the repair normally takes place at 9–12 months old. Before surgery, a polysomnography with a palatal plate in place is needed; this may predict the postoperative situation and gives insight on the chance of the presence of sleep apnea (OSAS) after the operation.^[8][32][33]
• Hearing loss is treated by bone conduction amplification, speech therapy, and educational intervention to avoid language/speech problems. The bone-anchored hearing aid is an alternative for individuals with ear anomalies^[34]
• Zygomatic and orbital reconstruction is performed when the cranio-orbitozygomatic bone is completely developed, usually at the age of 5–7 years. In children, an autologous bone graft is mostly used. In combination with this transplantation, lipofilling can be used in the periorbital area to get an optimal result of the reconstruction.; reconstruction of the lower eyelid coloboma includes the use of a myocutaneous flap, which is elevated and in this manner closes the eyelid defect.^[35]
• External ear reconstruction is usually done when the individual is at least eight years old. Sometimes, the external auditory canal or middle ear can also be treated.
• The optimal age for the maxillomandibular reconstruction is controversial; as of 2004, this classification has been used:^[8]

1. Type I (mild) and Type IIa (moderate) 13–16 years
2. Type IIb (moderate to severe malformation) at skeletal maturity
3. Type III (severe) 6–10 years

• When the teeth are cutting, the teeth should be under supervision of an orthodontist to make sure no abnormalities occur. If abnormalities like dislocation or an overgrowth of teeth are seen, appropriate action can be undertaken as soon as possible.^[16]
• Orthognatic treatments usually take place after the age of 16 years; at this point, all teeth are cut and the jaw and dentures are mature. Whenever OSAS is detected, the level of obstruction is determined through endoscopy of the upper airways. Mandibular advancement can be an effective way to improve both breathing and æsthetics, while a chinplasty only restores the profile.^[8]
• If a nose reconstruction is necessary, it is usually performed after the orthognatic surgery and after the age of 18 years.^[8]
• The contour of the facial soft tissues generally requires correction at a later age, because of the facial skeletal maturity. The use of microsurgical methods, like the free flap transfer, has improved the correction of facial soft tissue contours.^[36] Another technique to improve the facial soft tissue contours is lipofilling. For instance, lipofilling is used to reconstruct the eyelids.^[35]

Hearing loss

Hearing loss in Treacher Collins syndrome is caused by deformed structures in the outer and middle ear. The hearing loss is generally bilateral with a conductive loss of about 50-70 dB. Even in cases with normal auricles and open external auditory canals, the ossicular chain is often malformed.^[37]

Attempts to surgically reconstruct the external auditory canal and improve hearing in children with TCS have not yielded positive results.^[38]

Auditory rehabilitation with bone-anchored hearing aids (BAHAs) or a conventional bone conduction aid has proven preferable to surgical reconstruction.^[34]

Epidemiology

TCS occurs in about one in 50,000 births in Europe.^[4]

History

The syndrome is named after Edward Treacher Collins (1862–1932), the English surgeon and ophthalmologist who described its essential traits in 1900.^[5][6][39] In 1949, Adolphe Franceschetti and David Klein described the same condition on their own observations as mandibulofacial dysostosis. The term mandibulofacial dysostosis is used to describe the clinical features.^[40]

Media portrayals

A July 1977 New York Times article^[41] that was reprinted in numerous newspapers nationwide over the ensuing weeks, brought this malady to many people's attention for the first time.

The disorder was featured on the show Nip/Tuck, in the episode "Blu Mondae".^[42]

TLC's Born Without a Face^[43] features Juliana Wetmore, who was born with the most severe case in medical history of this syndrome and is missing 30%–40% of the bones in her face.^[43]

In 2010, BBC Three documentary Love Me, Love My Face^[44] covered the case of a man, Jono Lancaster, with the condition. In 2011, BBC Three returned to Jono to cover his and his partner Laura's quest to start a family,^[2] in So What If My Baby Is Born Like Me?,^[45] which first aired as part of a BBC Three season of programmes on parenting.^[46] The first film was replayed on BBC One shortly ahead of the second film's initial BBC Three broadcast. Lancaster's third BBC Three film, Finding My Family on Facebook,^[47] which looked at adoption, aired in 2011.

In Wonder, the children's novel, the main character is a child who has Treacher Collins Syndrome.^[48]

See also

• First arch syndrome
• Franceschetti-Klein syndrome
• Hearing loss with craniofacial syndromes

References

External links

• Reflections on Treacher Collins Syndrome
• a Personal View of Treacher Collins Syndrome
• a Map to help TCS People find each other
• Children's Craniofacial Association