Relating to the collar bone and to the cranium (bones of the skull which contain the brain): In medical school, Jeff learned about cleidocranial disorders affecting the bones in the skull and the clavicle.

A genetic disorder of bone development that is characterized by absent or incompletely formed collarbones and cranial and facial abnormalities that may include a square skull, late closure of the sutures of the skull, late closure of the fontanels (soft spots; skin and membrane-covered spaces remaining at the junction of the sutures, especially between the frontal and parietal bones in the incompletely covered skull), low nasal bridge, delayed eruption of the teeth, and abnormal permanent teeth.

A child with this disorder can bring his or her shoulders together, or nearly so. The gene for cleidocranial dysostosis has been found on chromosome six in band p21.