Medically, abnormal development or growth of a part of the body; such as, an organ, bone, or cell, including the total absence of such a part: "One example of dysplasia is in the respiratory tract in smokers or retinal dysplasia in the abnormal formation of the retina (back of the eyeball) during embryonic (pre-birth) development."

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.

A disease of bone marked by the thinning of the cortex and replacement of bone marrow by gritty fibrous tissue containing bony spicules (sharp-pointed pieces), producing pain, disability, and gradually increasing deformity.

Only one bone may be involved (fibrous dysplasia, monostotic) or several (fibrous dysplasia, polyostotic).

Fibrous dysplasia of bone involving only one bone.

Fibrous dysplasia of bone affecting several or many bones.

When associated with melanotic pigmentation of the skin and endocrine disorders, it is known as Albright's syndrome; which is a condition of cystic bone growth that results from abnormal bone development. It may occur with bone lesions, skin pigmentation, and endocrine abnormalities.

A severe form of neonatal dwarfism with very short limbs.

All cases have died at birth or in the neonatal period (first four weeks after birth).