Osteopetrosis: from animal models to human conditions

The term “osteopetrosis” is applied to a group of disorders characterized by an increased bone density, due to an inadequate bone resorption. A considerable part of our current knowledge on osteoclast biology is based on the study of osteopetrotic animal models. The search for mutations in these animals has unveiled many molecular mechanisms underlying osteoclast differentiation and functioning. It also supplied new candidate genes for the identification of genes involved in the human variants of this disease. All osteopetrotic genes identified so far in humans have their animal counterpart. The reverse is not true. This can partially be explained by the fact that still more than 30% of all patients suffer from osteopetrosis with an unkown molecular defect. Therefore, the studies of the osteopetrotic animal models and the correlating human osteopetrotic forms were and are still very important for our knowledge of the aetiology, prognosis and treatment of this disease. This review focuses on osteopetrotic animal models as well as human osteopetrotic conditions and their impact on osteoclast biology, pathogenesis and treatment.