Treacher Collins syndrome

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Treacher Collins syndrome

Definition

Treacher Collins syndrome (TCS) is a genetic disorder involving abnormal facial development. Individuals with TCS have underdevelopment of the jawbone, cheekbones, ears, and eye area. These features range widely from mild to severe. Intelligence and lifespan are usually normal.

Description

TCS was first described by E. Treacher Collins in 1900 after observation of two individuals with similar facial abnormalities. In 1940, Franceschetti and Klein gave TCS another name, mandibulofacial dysostosis. TCS is also sometimes called Franceschetti-Klein syndrome or Franceschetti syndrome.

The features of TCS result from a problem in early embryonic development. After an embryo forms, there are cells that are unspecialized and have the ability to develop into any type of cell in any part of the body (neural crest cells). Early in development, the neural crest cells travel to different areas of the embryo and specialize to become a specific type of cell for a specific organ or body part. The branchial arches is the area where neural crest cells specialize to develop the bone structure and features of the face. In individuals with TCS there is thought to be an error in the movement of the neural crest cells to the branchial arches or in the specialization of those cells once they reach the branchial arches. The result is underdevelopment of the facial bones, eyes, and ears.

Individuals with mild features of TCS may go undiagnosed. Sometimes adults do not know they have TCS until they have a child with more noticeable features. This can cause feelings of guilt for the parent. Children with more moderate to severe features of TCS look strikingly different and may be teased or shunned. These children are at risk for psychological stress and low self-esteem. Even adults with TCS who are productive and successful may battle issues of social stigma and low self-esteem regarding their facial differences.

Genetic profile

TCS is an autosomal dominant condition. Children of an affected parent have a 50% chance of inheriting the disorder. Males and females are affected equally. The severity of symptoms ranges widely, even among members of the same family. Therefore, the severity of a child's features cannot be predicted by the features of the affected parent.

About 40% of babies born with TCS have one affected parent. The other 60% are assumed to have a new, sporadic gene mutation (alteration). If a child has a new mutation (one that is not carried by the parents) then his or her siblings will have an extremely low chance of also having TCS. When a baby with TCS is born to seemingly normal parents, it is important to examine both parents carefully for mild features of TCS in order to give them accurate recurrence risks.

The gene for TCS is on chromosome 5 and is called TCOF1. This gene produces a protein that has been named treacle. Disease-causing TCOF1 mutations result in absent or inactive treacle. The exact role of treacle is not known but it is thought to be involved in early embryo neural crest cell movement or specialization in the branchial arches.

Demographics

TCS is rare and affects an estimated one in 25,000 to 50,000 live births.

Signs and symptoms

TCS is described as a craniofacial condition because its features are all related to the head and face. The overall head size may be smaller than average (microcephaly). The outer corners of the eyes slant downward. There may be colobomas on the lower eyelids, giving the lids a droopy appearance. The bridge of the nose is usually wide. Most individuals with TCS have underdeveloped cheekbones (malar bones) which give that area of the face a flat or sunken appearance. The lower jaw and chin are usually small and retroverted (jawbone points downward toward the neck instead of pointing out perpendicular to the neck). Many individuals also have a large mouth. Cleft palate (with or without cleft lip) is seen in one-quarter to one-third of patients with TCS.

Ear abnormalities are also common in TCS. The ears may be low-set, small, misshapen, or absent. For this reason, hearing loss or deafness is a common feature of TCS. The hearing loss is usually due to abnormalities in the middle ear structures rather than the outer ear structures.

Infants with moderate or severe malar bone underdevelopment may have compressed airways. These babies can have problems breathing after birth and may need a respirator or tracheostomy. A small, retroverted jaw and chin can cause feeding problems that may warrant a feeding tube.

The severity of features present at birth remains constant throughout life. TCS does not get progressively better or worse as an individual ages.

Diagnosis

The diagnosis of TCS is usually made by physical examination and identification of the typical facial features. Computerized tomography (CT scans) can be used to determine the degree of underdevelopment of the facial bone structure.

There are other syndromes that have facial appearances that resemble TCS. A complete physical examination of other body systems can help to establish a diagnosis of TCS. TCS can be distinguished from Nager syndrome and Miller syndrome if no abnormalities are present in the hands or arms. TCS can be distinguished from oculoauriculovertebral (OAV) conditions (for example, Goldenhar syndrome ) because facial involvement is bilateral (affecting both sides of the face) and the spinal column is normal.

If there are several people in a family with TCS, genetic linkage studies can be performed. Linkage studies require blood samples from many family members, both affected and unaffected. Markers on the TCOF1 gene are analyzed and compared to determine which gene version is shared by affected family members. The disease-causing gene should be present in all affected family members and absent from all unaffected members. Linkage studies can be performed on an unborn baby to determine if the baby inherited the family's disease-causing gene. Prenatal ultrasound can also be used to look for facial features of TCS. While there have been reports of prenatal diagnosis of TCS with ultrasound only, babies with mild features may appear normal. Detection may also depend on the skill of the physician performing the ultrasound and his or her experience with features of TCS.

Treatment and management

Newborn infants with severe TCS may require a ventilator, tracheostomy, or feeding tube if life-threatening breathing or feeding problems exist. A cleft palate can be repaired with surgery. Hearing aids can help individuals with hearing loss.

For most individuals, the problems of TCS are largely cosmetic. Plastic surgery can help to build the bone structure of the face, which may improve appearance as well as breathing and feeding. Surgeons can use bone grafts to build up the underdeveloped cheekbones. The jawbone can be "lengthened" and its angle repositioned. The bridge of the nose can be narrowed. Ears can be reconstructed using cartilage from the ribcage. Surgery can also be performed on the eye area.

This reconstruction may take multiple surgeries at different ages. Each individual must be evaluated for his or her unique features and needs. Surgeries are timed with facial growth and emotional needs and maturity of the patient.

Prognosis

A small percentage of newborns with TCS will have life-threatening breathing difficulties, and infant deaths can occur. However, the majority of individuals with TCS have a normal lifespan.

Resources

PERIODICALS

Dixon, M.J. "Treacher Collins Syndrome." Journal of Medical Genetics 32 (1995): 806–08.

Posnick, J.C., and R.L. Ruiz. "Treacher Collins Syndrome: Current Evaluation, Treatment, and Future Directions." Cleft Palate-Craniofacial Journal 37, no. 5 (September 2000): 483+.

ORGANIZATIONS

FACES: The National Craniofacial Association. PO Box 11082, Chattanooga, TN 37401. (423) 266-1632 or (800) 332-2373. [email protected]. <http://www.faces-cranio.org/>.

Treacher Collins Foundation. Box 683, Norwich, VT 05055. (800) 823-2055.