SP7 and Osteopenia: However, a previous study showed that osteoblast-specific deletion of Osx driven by this 2.3 kB Col1a1 promoter does not cause clear bone defects in embryos and newborn pups but leads to osteopenia phenotypes in growing mice, including decreased BMD in the lumbar vertebra, thinner cortex of long bones, and immature trabecular bones [15].