Treacher Collins Syndrome

What Is a Cleft Palate or Cleft Lip?

Cleft palate and cleft lip are birth defects that involve the upper lip and roof of the mouth. They can occur together or separately. These malformations happen because of an incomplete fusion as the lip develops (at 35 days gestation) or the incomplete fusion of the developing lip (normally occurring by the 8th to 9th weeks of gestation). Gender and ethnicity are risk factors for these birth defects, but there also are other factors that seem to play a role in these defects.

Treacher Collins syndrome definition and facts*

*Treacher Collins syndrome facts medically edited by: Charles Patrick Davis, MD, PhD

  • Treacher Collins syndrome (TCS) is a condition (genetic disease) that alters the development of bones and other tissues in the face.
  • Signs and symptoms vary from almost unnoticeable face changes to severe facial and ear alterations, cleft palate and restricted airway
  • Characteristics of TCS include craniofacial or mandibulofacial abnormalities:
    • Eyes that slant downward away from the nose
    • Very few eyelashes and a notch in the lower eyelids (coloboma eye)
    • Ears that are absent or unusually formed
    • Some individuals may have hearing loss
    • A small jaw
  • A child with TCS may have sleep apnea and/or conductive hearing loss; the loss of ear function may require a resource to provide child hearing aids.
  • Some individuals can be affected severely, and they may develop life-threatening breathing problems (infantile apnea).
  • Other abnormalities may make breathing and feeding difficult for a child due to the narrowed obstruction of the nasal airways.
  • A child may have features of “Pierre Robin sequence,” in which the tongue is located farther back in the throat than normal (glossoptosis), with or without and incomplete cleft palate of the mouth and airway obstruction.

What is Treacher Collins syndrome?

Treacher Collins is a condition that affects the development of bones and other tissues in the face.

What are the signs and symptoms of Treacher Collins syndrome?

The signs and symptoms of this disorder vary greatly, ranging from almost unnoticeable to severe. Most individuals have:

  • underdeveloped facial bones,
  • particularly the cheek bones, and
  • A very small jaw and chin (micrognathia).

Some people with this condition are also born with an opening in the roof of the mouth called a cleft palate. In severe cases, underdevelopment of the facial bones may restrict an affected infant's airway, causing potentially life-threatening respiratory problems.

What are the characteristics of Treacher Collins syndrome?

  • People with TCS often have eyes that slant downward, sparse eyelashes, and a notch in the lower eyelids called an eyelid coloboma.
  • Some individuals have additional eye abnormalities that can lead to vision loss.
  • It also characterized by absent, small, or unusually formed ears.
  • Hearing loss occurs in about half of all individuals with the problem; hearing loss is caused by defects of the three small bones in the middle ear, which transmit sound, or by underdevelopment of the ear canal.
  • People with Treacher Collins usually have normal intelligence.

How common is this syndrome?

Treacher Collins affects an estimated 1 in 50,000 people.

How do you get Treacher Collins (Causes)?

When Treacher Collins results from mutations in the TCOF1 or POLR1D gene, it is considered an autosomal dominant condition, which means one copy of the altered gene in each cell is sufficient to cause the disorder. About 60 percent of these cases result from new mutations in the gene and occur in people with no history of the disorder in their family. In the remaining autosomal dominant cases, a person with TCS inherits the altered gene from an affected parent.

When TCS is caused by mutations in the POLR1C gene, the condition has an autosomal recessive pattern of inheritance. Autosomal recessive inheritance means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

What genes are related to this syndrome?

Mutations in the TCOF1, POLR1C, or POLR1D gene can cause Treacher Collins. TCOF1 gene mutations are the most common cause of the disorder, accounting for 81 to 93 percent of all cases. POLR1C and POLR1D gene mutations cause an additional 2 percent of cases. In individuals without an identified mutation in one of these genes, the genetic cause of the condition is unknown.

The proteins produced from the TCOF1, POLR1C, and POLR1D genes all appear to play important roles in the early development of bones and other tissues of the face. These proteins are involved in the production of a molecule called ribosomal RNA (rRNA), a chemical cousin of DNA. Ribosomal RNA helps assemble protein building blocks (amino acids) into new proteins, which is essential for the normal functioning and survival of cells. Mutations in the TCOF1, POLR1C, or POLR1D gene reduce the production of rRNA. Researchers speculate that a decrease in the amount of rRNA may trigger the self-destruction (apoptosis) of certain cells involved in the development of facial bones and tissues. The abnormal cell death could lead to the specific problems with facial development found in TCS. However, it is unclear why the effects of a reduction in rRNA are limited to facial development.

Medically Reviewed by a Doctor on 2/7/2017

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