Mandibulofacial dysostosis, also known as Treacher Collins syndrome (TCS; entry 154500 in the Online Mendelian Inheritance in Man [OMIM] classification system), is an inherited developmental disorder with a prevalence estimated to range between 1 in 40,000 to 1 in 70,000 of live births.
Growth of craniofacial structures derived from the first and second pharyngeal arch, groove, and pouch is diminished symmetrically and bilaterally.
The condition is recognizable at birth and can also be diagnosed prenatally based on ultrasonography findings. The following images are examples of the characteristic features of this condition.
Also known as Treacher Collins syndrome, mandibulofacial dysostosis (MFD) is a rare syndrome characterized by underdeveloped facial bones and a very small lower jaw and chin, called micrognathia.
The most obvious facial differences are the underdeveloped cheekbones and the drooping lower eyelids. Some children with MFD also have a cleft palate.
The child’s ears may be normal, or they may be small, malformed or missing altogether, and hearing impairment is often part of the syndrome.
Most children with MFD have complications related to speech, hearing, vision, swallowing and breathing.
In severe cases, underdeveloped facial bones may restrict an infant’s airway, causing potentially life-threatening respiratory problems that may require a tracheotomy, a surgical procedure to open the windpipe.
MFD is a genetic condition that follows an autosomal dominant inheritance pattern, meaning if one parent has the syndrome, they have a 50 percent chance of passing it on to their child. It can also result from a spontaneous genetic mutation in the person with the syndrome.
This person will then have a 50 percent chance of passing the condition on to his or her children.
During the developmental stage, the embryo undergoes a series of transformations that form a template for the development of organs and processes.
A group of such processes are responsible for the development of most of the structures involved in the head and neck the branchial arches. These are 6 in number, but essentially five of them are functional as the fifth arch is rudimentary.
The first arch is called the mandibular arch and this is the main focus in Treacher Collins syndrome. Defects in this arch lead to the development of the syndrome in future.
Signs and Symptoms
Mandibulofacial Dysostosis is characterized by a wide variety of clinical features depending on the branchial arches involved in the developmental malformation.
The first thing that is apparent on looking at a person affected by the condition is the presence of anti-mongoloid palpebral fissures and the partially absent eyelids.
Sometimes the eyelashes are completely absent. There is a deficient growth in facial bones especially that of the mandible or the lower jaw and the malar bones, also called the cheek bones.
This results in a narrow facial structure giving the patient a characteristic appearance referred to as the Parrot Beak appearance.
A diagnosis of Mandibulofacial Dysostosis is made on clinical grounds and is confirmed by X-ray, which typically demonstrate the thin bones especially in the facial region.
Treatment for MFD depends on the child’s age and the severity of the condition. In infancy, breathing and eating problems will be monitored.
Sometimes, a tracheotomy — a breathing tube placed in the windpipe — is required to help the child breathe. If the child has a cleft palate, surgery to repair the cleft may be performed at around 1 year of age.
Hearing management is extremely important and children should be seen by an audiologist (hearing specialist) and otolaryngologist (ear, nose and throat doctor).
CT scans can help determine whether surgery to restore hearing is likely to be successful. Most children and adults with MFD will need hearing aids.
Some children with MFD have speech difficulties and will need to see a speech therapist. The speech problems may be related to a repaired cleft palate or to hearing loss.
In addition, most children with MFD will need extensive orthodontic treatment.
Other treatments may include surgery on the ears, lower eyelids, cheekbones and jaws, to improve both function and appearance.