Mandibulofacial dysostosis, also known as Treacher Collins Syndrome (TCS), is a rare, congenital condition affecting the development of facial bones and tissues, particularly the cheekbones, jaw, and ears. It is characterized by distinctive facial differences, with severity varying among individuals.
Genetic Origin
Treacher Collins Syndrome primarily stems from mutations in specific genes, most commonly TCOF1, but also POLR1C and POLR1D. The TCOF1 gene, located on chromosome 5, provides instructions for creating a protein called treacle, which is important for the early development of facial bones and tissues. Its dysfunction can lead to the self-destruction of cells important for facial development. Mutations in POLR1C and POLR1D genes account for approximately 2% of cases.
The inheritance pattern of Treacher Collins Syndrome is most often autosomal dominant, meaning one altered gene copy is sufficient to cause the condition. An affected parent has a 50% chance of passing the altered gene to each child. However, around 60% of cases result from new (de novo) gene mutations, meaning the individual has no family history. While TCOF1 and POLR1D mutations usually follow an autosomal dominant pattern, POLR1C mutations can lead to an autosomal recessive inheritance, requiring altered copies from both parents.
Characteristic Features
Individuals with Treacher Collins Syndrome exhibit distinctive physical characteristics, primarily affecting the craniofacial region. These include underdeveloped facial bones, particularly the cheekbones, which can give the mid-face a sunken appearance. The lower jaw and chin may also be small (micrognathia), leading to a recessed chin and an overbite. Eyes often have a downward slant, sparse eyelashes, and a notch in the lower eyelids (eyelid coloboma).
Ear anomalies are frequently observed, ranging from small or unusually shaped ears (microtia) to absent ears. The external ear canal may be narrow or missing, affecting hearing. Conductive hearing loss, caused by malformations of the outer and middle ear structures or the bones within the middle ear, affects about 50% of individuals with TCS. While inner ear structures are typically unaffected, issues with sound transmission can impair hearing.
Beyond facial appearance, TCS characteristics can lead to functional challenges. A small jaw may cause tongue retraction, obstructing the airway and leading to breathing difficulties, especially in infants, sometimes resulting in sleep apnea. A cleft palate is common in about 25% of affected individuals, impacting feeding and speech development. Vision problems can arise from eye abnormalities, including strabismus (crossed eyes), refractive errors, or dry eyes due to lower eyelid issues. The severity of these features varies widely, from mild to severe and potentially life-threatening.
Identification and Support
Identification of Treacher Collins Syndrome can occur at different stages. Prenatal diagnosis may be suspected through ultrasound examinations revealing characteristic facial features, with genetic testing confirming the diagnosis. After birth, medical professionals suspect TCS based on distinctive physical characteristics like underdeveloped facial bones and ear malformations. Genetic testing for mutations in TCOF1, POLR1C, or POLR1D genes then confirms the diagnosis, especially when physical features are less pronounced or uncertain.
Managing Treacher Collins Syndrome involves a comprehensive, multidisciplinary approach. Surgical interventions are important, aiming to reconstruct facial bones like the jaw and cheekbones, and address issues such as cleft palate. These surgeries are often staged as the child grows. Audiological management is a priority, with hearing aids or bone-anchored hearing systems (BAHAs) commonly used to address conductive hearing loss.
Speech therapy is frequently recommended for speech development affected by hearing loss or a cleft palate. Feeding support is provided for infants with difficulty feeding due to a small jaw or cleft palate, sometimes requiring feeding tubes. Ophthalmologic care addresses vision problems and eye abnormalities, including dry eyes or strabismus. This coordinated care, involving specialists like plastic surgeons, audiologists, speech-language pathologists, and ophthalmologists, addresses functional and aesthetic aspects, supporting overall well-being.
Life with Treacher Collins
Individuals with Treacher Collins Syndrome generally possess normal intelligence and can participate fully in academic and social environments. While the condition presents physical challenges, particularly facial differences, individuals can lead fulfilling lives. Ongoing medical care and support are important throughout life, as needs evolve from childhood into adulthood, helping manage persistent physical challenges and promoting overall health.
Adaptive strategies are employed to help individuals navigate daily life and achieve their potential. These strategies range from specialized feeding techniques in infancy to assistive hearing devices and speech therapy as they grow. The focus remains on enhancing quality of life and fostering independence. Despite visible characteristics, the emphasis is on the individual’s capabilities and personal growth.