Sclerosing bone disorders: too much of a good thing

Osteoporosis is, because of its high prevalence and morbidity, a major health problem in our aging population. Epidemiological studies clearly indicated a heritability of up to 80% for relevant bone parameters with an additional role for environmental factors, such as food intake and physical exercise. A major contribution to our current understanding of bone homeostasis is obtained by studying monogenic diseases with an increased bone density, the sclerosing bone dysplasias. Gene identifications have revealed relevant pathways and mechanisms both in the bone-resorbing osteoclasts and bone-forming osteoblasts. Furthermore, natural variants within these genes turned out to have an influence on bone mineral density in the general population. Finally, interesting drug targets for the prevention and treatment of osteoporosis were revealed. Although many major breakthroughs have been realized, still a huge amount of significant information is hidden in these pathologies as the function of many of these genes and newly identified pathways is not, or only partially, clear.