Bone mineral density (BMD) is a quantitative trait for which the heritability of the variance is estimated to be up to 80%, based on epidemiological and twin studies. Further illustration of the involvement of genetic factors in bone homeostasis, is the existence of an extended group of genetic conditions associated with an abnormal bone density. The group of conditions with increased bone density has long been poorly studied and understood at the molecular genetic level but recently, thanks to recent developments in molecular genetics and genomics, for some of them major breakthroughs have been made. These findings will make the molecular analysis of such patients an additional tool in diagnostics and in genetic counseling. However, the initial identification of affected patients is still largely dependent upon recognition of clinical and radiological stigmata of the disease. Therefore, in this overview of sclerosing bone dysplasias, the classical clinical and radiological signs of this group of disorders win be discussed along with the new molecular insights. (C) 2001 Elsevier Science Ireland Ltd All rights reserved.
