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Cleidocranial dysplasia (CCD), also known as cleidocranial dysostosis, is a hereditary condition characterized by abnormal clavicles, delayed fusion of the bones in the skull, extra teeth, short stature, and other skeletal changes.
CCD involves a characteristic group of abnormalities affecting primarily the skull, teeth, and clavicles. Other bones, such as the ribs, pelvis, and bones of the hands and feet may also be affected. Older children and adults with CCD are typically shorter than average. Most individuals with this condition do not have significant physical or mental disability.
CCD is an autosomal dominant condition with variable expressivity (variable symptoms) and complete penetrance (meaning that all individuals who carry the gene for CCD have some symptoms). It is estimated that one third of cases represent new mutations, or genetic changes. The gene responsible for CCD has been mapped to the short arm of chromosome 6 and is called CBFA1. This gene encodes a transcription factor, meaning a protein that regulates DNA transcription, and is specifically expressed in the bone. Mutations in CBFA1 have been identified in many individuals and families with CCD.
More than 500 cases of CCD among individuals of various ethnic backgrounds have been described in the medical literature. The incidence of CCD is reported to be highest around Cape Town, South Africa. The number of affected individuals in this area was estimated to exceed 1,000 as of 1996. These individuals descended from an affected Chinese sailor who settled in the area in 1896 and had seven wives. Study of this large family helped localize the gene responsible for the condition.
Individuals with CCD typically show a delay or failure of the fusion of the calvarial sutures, the openings between the bones of the skull in infants. In some cases, the anterior fontanelle (the "soft spot" on an infant's head) or other areas of the skull may remain unfused through life. A typical facial appearance in persons with CCD includes a broad forehead and widely spaced eyes. The overall head size is usually at the upper limit of normal.
Almost all persons with CCD have some degree of hypoplasia, or underdevelopment, of the clavicles (collar bones). In severe cases, both clavicles may be absent. More commonly, there is hypoplasia of the outside end of the clavicles. Depending on the degree of severity of clavicular hypoplasia, the external appearance of the shoulder may be affected. Some persons with CCD appear to have narrow, sloping shoulders, and some have the unusual ability to bring their shoulders together beneath their chin. This defect usually does not result in physical disability for the individual.
Dental abnormalities are very frequent among persons with CCD and are considered characteristic of the
Other signs of CCD include a small rib cage with short or abnormal ribs. The vertebra of the spine may be malformed. The pelvis may be underdeveloped, with an increased space between the pubic bones. The growth of the bones in the hands and feet are often abnormal; most are shorter but others are longer than normal. Final height in adults with CCD is usually shorter than expected given the family background.
Author Info: Jennifer Roggenbuck MS, CGC, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Genetic Disorders Part II, 2005This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.
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