Treacher Collins syndrome
Treacher Collins syndrome is a genetic condition affecting the development of facial bones and tissues, often resulting in distinct facial features and potential hearing or respiratory challenges.
Overview
Treacher Collins syndrome affects the development of bones and other tissues of the face. The severity of signs and symptoms varies greatly. Most affected individuals have underdeveloped facial bones, particularly the cheekbones, and a very small jaw and chin (micrognathia). Some individuals are born with an opening in the roof of the mouth (cleft palate).
Symptoms
Common features of the condition include:
- Downward-slanting eyes
- Sparse eyelashes and a notch in the lower eyelids (eyelid coloboma)
- Absent, small, or unusually formed ears
- Hearing loss (caused by defects in the middle ear or ear canal)
In severe cases, underdeveloped facial bones may restrict an infant's airway, causing life-threatening respiratory problems. Most people with this syndrome have normal intelligence.
Causes & Risk Factors
Variants in the TCOF1, POLR1C, or POLR1D genes cause the syndrome. These genes produce proteins essential for the early development of facial bones and tissues by helping to produce ribosomal RNA (rRNA). A reduction in rRNA is thought to trigger the self-destruction (apoptosis) of cells involved in facial development.
Inheritance
The inheritance pattern depends on the specific gene involved:
- Autosomal dominant: Variants in TCOF1 or POLR1D. One copy of the altered gene is sufficient to cause the disorder. About 60 percent of these cases result from new mutations in the gene in people with no family history.
- Autosomal recessive: Variants in POLR1C. Both copies of the gene in each cell must have variants to cause the disorder. Parents of an affected individual typically do not show signs of the condition.