Cleidocranial Dysostosis

Cleidocranial dysostosis (CCD), also known as cleidocranial dysplasia, is a congenital condition primarily affecting the bones and teeth. The disorder is characterised by poorly developed or absent collarbones, allowing the shoulders to be brought unusually close together.

The front of the skull often closes later than normal, and affected individuals are typically shorter than average. Other common features include a prominent forehead, wide-set eyes, abnormal teeth, and a flat nasal bridge. Intelligence is generally unaffected.

Signs and Symptoms

CCD is a skeletal condition named after its hallmark features: collarbone (cleido-) and cranium deformities. Patients often present with painless swelling in the clavicle area around the age of 2–3 years. The clavicles may be partially or completely missing, leading to hypermobility of the shoulders. In severe cases, partial collarbones may cause nerve damage symptoms necessitating surgical removal.

Other features include a prognathic mandible due to maxillary hypoplasia, delayed closure of the cranial fontanelles, and underdeveloped bones and joints, resulting in shorter stature and smaller frames. Dental abnormalities such as supernumerary teeth, crowding, displaced teeth, and deficient cementum formation are common. Additional signs include a bossing forehead, hypertelorism, widened symphysis pubis, coxa vara, vertebral abnormalities, scoliosis, and spina bifida. Patients may also experience a high risk of hearing loss, decreased bone density, and increased risk of fractures.

Genetics

CCD is usually inherited in an autosomal dominant manner but can also occur due to new mutations. The condition is primarily caused by mutations in the RUNX2 gene located on chromosome 6 (6p21). This gene encodes a transcription factor essential for osteoblast differentiation, leading to delayed ossification of midline structures and defects in bone formation.

Diagnosis

Diagnosis is typically based on clinical signs and radiographic findings, with genetic testing confirming the condition. During pregnancy, clavicular size can be estimated using nomograms. Radiological imaging may show open skull sutures, large fontanelles, multiple wormian bones, and underdeveloped paranasal sinuses.

Treatment

Treatment focuses on supportive care, such as protective headgear for open fontanelles and dental interventions for supernumerary teeth. Surgical correction may be necessary around age 5 to prevent deformity progression. Craniofacial surgery can address skull defects, and corrective femoral osteotomies can treat coxa vara. Excision of clavicular fragments may alleviate brachial plexus irritation.

Prognosis

Life expectancy for individuals with CCD is generally normal.

Epidemiology

CCD affects approximately one in a million individuals, with equal prevalence in males and females.

Notable Cases

Notable individuals with CCD include actor Gaten Matarazzo and sibling actress-singers Milly and Abby Shapiro. The condition has also been integrated into the character Dustin Henderson's storyline in the television show Stranger Things.

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Self-assessment MCQs (single best answer)

What is the primary cause of cleidocranial dysostosis (CCD)?

Which of the following is a common feature of CCD?

What type of inheritance pattern does CCD usually follow?

Which skeletal structure is typically underdeveloped or missing in individuals with CCD?

Which of the following is NOT a common dental abnormality associated with CCD?

What is the main diagnostic method for confirming CCD?

What condition may individuals with CCD experience a high risk of?

Which treatment is NOT typically used for managing CCD?

What is the expected life expectancy for individuals with CCD?

Which of the following individuals is known to have CCD?