Craniometaphyseal dysplasia: An inherited skeletal condition that involves abnormal bone formation and abnormal mineralization of the skull as well as the long bones. There is increased density of craniofacial bones beginning at the base of the skull during early childhood. The progressive thickening of the bones of the skull can lead to severe visual and neurological impairment, such as facial palsy and deafness. Typical facial features include a wide bridge of the nose and wide spacing of the eyes. The growth plates (metaphyses) of long bones are widened (Erlenmeyer flask-shaped) and show decreased density while the shafts of the long bones are thickened.
Craniometaphyseal dysplasia occurs in autosomal dominant and recessive forms. The dominant form due to one copy of the gene is more common and less severe. The gene in chromosome region 5p15.2-p14.1 is the ANK gene which encodes a protein involved in the transport of pyrophosphate into the bone matrix. Pyrophosphate levels are critical for the regulation of bone mineralization. The gene for the recessive form is in a different location, in chromosome region 6q21-22. Its function is not yet known.