Functional variants of RUNX2 related to bone density

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Bone density and osteoporosis have a genetic component. Identifying genes that are involved in determining bone density may permit advances in controlling osteoporosis. We have identified a variant in a gene called RUNX2 that is related to bone density high enough to protect individuals four fold against Colle's fracture, the common wrist fracture seen in women. This variant is highly correlated with changes in the second promoter of RUNX2, such that the high bone density form appears to be the ancestral form of this gene. We now need to know how this change in this promoter alters bone density and we are following up on observations that other important transcription factors bind to the variable site in the promoter. Furthermore, we have assembled a large collection of samples from people who have had extensive measures of bone density and arthritis in order to accurately measure the impact of this gene on bone density, osteoarthritis and bone fracture. In addition, some people with bone fracture at the hip, or low bone density, have mutations in this gene. Such mutations in a region called the Q-repeat are rather common, 1-200 people are carriers. Our data show that these mutant proteins are not as efficient at their task of regulating other genes. We now want to know how this occurs in a molecular sense, since it is known that the Runx2 protein resides in the nucleus of the cell and interacts with many other regulators. This part of the project is being done with one of the world experts on gene regulation in bone cells. Since RUNX2 is a master regulator of the cells that make bone, this gives hope that it may be possible to alter bone formation through this master regulator.