In individuals without an identified variant in one of these genes, the genetic cause of the condition is unknown. POLR1C and POLR1D gene variants cause an additional 2 percent of cases.

TCOF1 gene variants are the most common cause of the disorder, accounting for 81 to 93 percent of all cases. Variants (also known as mutations) in the TCOF1, POLR1C, or POLR1D gene can cause Treacher Collins syndrome. People with Treacher Collins syndrome usually have normal intelligence. Hearing loss occurs in about half of all affected individuals 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. This condition is also characterized by absent, small, or unusually formed ears. Some affected individuals have additional eye abnormalities that can lead to vision loss. People with Treacher Collins syndrome often have eyes that slant downward, sparse eyelashes, and a notch in the lower eyelids called an eyelid coloboma. In severe cases, underdevelopment of the facial bones may restrict an affected infant's airway, causing potentially life-threatening respiratory problems. Some people with this condition are also born with an opening in the roof of the mouth called a cleft palate. Most affected individuals have underdeveloped facial bones, particularly the cheek bones, and a very small jaw and chin (micrognathia). The signs and symptoms of this disorder vary greatly, ranging from almost unnoticeable to severe. Treacher Collins syndrome is a condition that affects the development of bones and other tissues of the face.

Free download facial bones