Treacher-Collins syndrome affects the development of bone and other tissues of the face. The signs and symptoms of this disorder can vary greatly, ranging from almost unnoticeable to severe. Most victims have underdeveloped facial bones, particularly cheekbones, and a very small jaw and chin (in newborns). Some people with Treacher Collins syndrome are born with a hole in their mouth called a "cleft palate". In severe cases, underdevelopment of the facial bones can restrict the victim's airway, causing potentially life-threatening illnesses.
Often, people with this disease have downward tilted eyes, sparse eyelashes, and a lower eyelid defect called a coloboma. This causes additional ophthalmic disturbances that can lead to loss of vision. In addition, there may be small or unusually shaped ears, or none. Hearing loss occurs in about half of the cases. It is caused by defects in the three small bones of the middle ear that transmit sound, or by the underdevelopment of the ear canal. The presence of Treacher-Collins syndrome does not affect intelligence: as a rule, itnormal.
What gene mutations cause Treacher-Collins syndrome?
The most common cause: mutations in the TCOF1, POLR1C or POLR1D genes. The TCOF1 gene mutation is the cause of 81-93% of all cases. POLR1C and POLR1D are an additional 2% of cases. In individuals without a specific mutation in one of the genes, the cause of the disease is unknown. The TCOF1, POLR1C, and POLR1D genes play an important role in the early development of bones and other tissues of the face. They are involved in the production of a molecule called ribosomal RNA (rRNA), the chemical cousin of DNA. Ribosomal RNA helps assemble protein blocks (amino acids) into new proteins, which are essential for normal cell function and survival. Mutations in the TCOF1, POLR1C, or POLR1D genes reduce rRNA production. Researchers believe that a decrease in the amount of rRNA can lead to the self-destruction of certain cells involved in the development of facial bones and tissues. Abnormal cell death can lead to certain problems with facial development in people with Treacher-Collins syndrome.
How is Treacher-Collins syndrome inherited?
If the disease occurs due to a mutation in the TCOF1 or POLR1D genes, it is considered to be an autosomal dominant disease. About 60% of cases of the disease result from new mutations in the gene and occur in people with no family history. In other cases, the syndrome is inherited through an altered gene from the parents.
When the disease is caused by mutations in the POLR1C gene, it is considered to be an autosomal recessive mode of inheritance. An individual's parentsautosomal recessive disease have one copy of the mutated genes, but they usually do not show signs and symptoms of the disease.
Syndrome Treatment
Treatment depends on the severity of the condition, but may include:
- genetic consultations - for an individual or the whole family, depending on whether the disease is hereditary or not;
- hearing aids - in case of conductive hearing loss;
- dental treatment, including orthodontic, aimed at correcting malocclusion;
- speech therapy classes to improve communication skills. Defectologists also work with people who have trouble swallowing food or drinks;
- surgical techniques to help improve appearance and quality of life.
