Treacher Collins syndrome: a genetic condition that results in a disorder of development of the bones and muscles of the face. The condition affects 1 out of about every 50,000 people and is due to a mutation in a gene known as TCOF1. It is inherited in an autosomal dominant manner, meaning that a person who has one copy of the defective gene will have the condition. However, about 60% of cases occur in people without a family history as a result of new mutations in the gene.
Symptoms of Treacher Collins syndrome range from mild and hardly noticeable to severe and disfiguring. Symptoms can include small and abnormally formed ears, underdeveloped facial bones, a very small jaw and chin (micrognathia), cleft palate, eyes that slant downward, sparse eyelashes, a notch in the lower eyelids called a coloboma, and hearing loss due to middle ear defects