What are the signs and symptoms of Treacher Collins syndrome? The signs and symptoms of Treacher Collins syndrome vary greatly, ranging from almost unnoticeable to severe. Most affected people 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. People with Treacher Collins syndrome often have eyes that slant downward, sparse eyelashes, and a notch in the lower eyelids called a coloboma. Some people have additional eye abnormalities that can lead to vision loss. The condition is also characterized by absent, small, or unusually formed ears. Defects in the middle ear (which contains three small bones that transmit sound) cause hearing loss in about half of affected people. People with Treacher Collins syndrome usually have normal intelligence.  You can read additional information about the features of Treacher Collins syndrome through MedlinePlus and GeneReviews. The Human Phenotype Ontology provides the following list of signs and symptoms for Treacher Collins syndrome. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Abnormality of bone mineral density 90% Dental malocclusion 90% Hypoplasia of the zygomatic bone 90% Malar flattening 90% Skeletal dysplasia 90% Small face 90% Abnormality of the pinna 77% Lower eyelid coloboma 69% Sparse lower eyelashes 53% Abnormality of the eyelashes 50% Atresia of the external auditory canal 50% Cleft eyelid 50% Conductive hearing impairment 50% Frontal bossing 50% Low anterior hairline 50% Reduced number of teeth 50% Strabismus 50% Visual impairment 50% Wide nasal bridge 50% Visual loss 37% Abnormality of the auditory canal 36% Cleft soft palate 32% Projection of scalp hair onto lateral cheek 26% Abnormality of cardiovascular system morphology 7.5% Abnormality of dental enamel 7.5% Abnormality of dental morphology 7.5% Abnormality of parotid gland 7.5% Abnormality of the adrenal glands 7.5% Abnormality of the thyroid gland 7.5% Aplasia/Hypoplasia affecting the eye 7.5% Aplasia/Hypoplasia of the thymus 7.5% Bilateral microphthalmos 7.5% Cataract 7.5% Choanal atresia 7.5% Cleft palate 7.5% Cleft upper lip 7.5% Cognitive impairment 7.5% Cryptorchidism 7.5% Encephalocele 7.5% Facial cleft 7.5% Glossoptosis 7.5% Hypertelorism 7.5% Hypoplasia of penis 7.5% Hypoplasia of the pharynx 7.5% Iris coloboma 7.5% Lacrimal duct stenosis 7.5% Multiple enchondromatosis 7.5% Narrow mouth 7.5% Neurological speech impairment 7.5% Patent ductus arteriosus 7.5% Preauricular skin tag 7.5% Ptosis 7.5% Respiratory insufficiency 7.5% Scrotal hypoplasia 7.5% Tracheoesophageal fistula 7.5% Trismus 7.5% Upper eyelid coloboma 7.5% Urogenital fistula 7.5% Wide mouth 7.5% Intellectual disability 5% Autosomal dominant inheritance - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.