Cleidocranial dysostosis

Cleidocranial dysostosis is a general skeletal condition so named from the collarbone (cleido-) and cranium deformities which people with it often have. People with the condition usually present with a painless swelling in the area of the clavicles at 2 to 3 years of age. Common features are: • Clavicles (collarbones) can be partly missing leaving only the medial part of the bone. In 10% of cases, they are completely missing. The defect is bilateral 80% of the time. Partial collarbones may cause nerve damage symptoms and therefore have to be removed by surgery. • The mandible is prognathic due to hypoplasia of maxilla (micrognathism) and other facial bones. • Failure of eruption of permanent teeth. • Bossing (bulging) of the forehead. • Open skull sutures, large fontanelles. • Hypertelorism. • Delayed ossification of bones forming symphysis pubis, producing a widened symphysis. • Coxa vara can occur, limiting abduction and causing Trendelenburg gait. • Short middle fifth phalanges, sometimes causing short and wide fingers. • Vertebral abnormalities. Other features are: parietal bossing, basilar invagination (atlantoaxial impaction), persistent metopic suture, abnormal ear structures with hearing loss, supernumerary ribs, hemivertebrae with spondylosis, small and high scapulae, hypoplasia of illiac bones, absence of the pubic bone, short / absent fibular bones, short / absent radial bones, hypoplastic terminal phalanges. ==Genetics==

CCD is usually autosomal dominant, but in some cases its cause is not known. The main mechanism is thought to involve haploinsufficiency caused by mutations in CBFA1 (also known as Runx2), a gene located on the short arm of chromosome 6 (6p21), which encodes a transcription factor required for the differentiation of stem cells into osteoblasts. This results in delayed ossification of midline structures of the body and ensuing defects in intramembranous and endochondral bone formation. ==Diagnosis==

Different features of the dysostosis are significant. Radiological imaging helps confirm the diagnosis. During gestation (pregnancy), clavicular size can be calculated using available nomograms. Wormian bones can sometimes be observed in the skull. Diagnosis of CCD spectrum disorder is established in an individual with typical clinical and radiographic findings and/or by the identification of a heterozygous pathogenic variant in RUNX2 (CBFA1). ==Treatment==

Around 5 years of age, surgical correction may be necessary to prevent any worsening of the deformity. If the mother has dysplasia, caesarian delivery may be necessary. Craniofacial surgery may be necessary to correct skull defects. Coxa vara is treated by corrective femoral osteotomies. If there is brachial plexus irritation with pain and numbness, excision of the clavicular fragments can be performed to decompress it. == Prognosis ==

Several studies have reported that life expectancy appears to be normal for people with CCD. ==Epidemiology==

Cleidocranial dysostosis affects about one per million people. ==Notable cases==

In 1987, a young girl named Jessica McClure fell down a narrow well pipe in her family's Texas property. Ron Short, a roofing contractor who was born without collarbones because of cleidocranial dysostosis and thus could collapse his shoulders to work in cramped corners, arrived at the site and offered to go down the shaft. The rescuers did not end up using him, though McClure was successfully recovered from the well. Actor Gaten Matarazzo was born with cleidocranial dysplasia, which is incorporated into his character Dustin Henderson's storyline on Stranger Things. Sibling actress-singers Milly and Abi Shapiro were born with cleidocranial dysplasia, a trait they share with their mother. ==References==