Cleidocranial dysplasia (CCD) is a condition characterized by defects in membranous and endochronal ossification resulting in skeletal abnormalities, most notably, partly or completely missing collarbones (clavicles), retention of deciduous teeth, delayed closing of the fontanels, and a shorter than normal stature. Only 10% of affected patients show a total absence of both clavicles. In most other cases, there is only partial agenesis of the collarbone. The retention of deciduous teeth leads to the presence of multiple supernumerary teeth. Other features seen in the condition include underdeveloped bones and joints, bulging of the forehead, hypertelorism, brachycephaly, pseudoprognathism, high arched palate, short, tapered fingers and broad thumbs, short forearms, flat feet; knock knees, scoliosis of the spine, conductive deafness with frequent episodes of otitis media, and absence of nasal bones. Affected individuals have a normal intelligence and life span.
Cleidocranial dysplasia can be easily diagnosed based on the triad of symptoms of agenesis of the clavicles, multiple supernumerary teeth, and open sagital sutures and fontanels. In cases where the supernumerary teeth have not been reabsorbed even by adolescence, they may have to be removed to prevent crowding in the jaw. Frequent ear infections may also require monitoring and management.
Cleidocranial dysplasia is inherited as an autosomal dominant condition, and is believed to be due to defects in the RUNX2 gene. This gene codes for a transcription factor, which in turn activates several genes involved in osteoblastic differentiation. Defects in the functioning of this protein, therefore, cause significant defects in bone and cartilage development, resulting in cleidocranial dysplasia. Yet, about 40% of cases of cleidocranial dysplasia have been reported to be sporadic, without any genetic cause.