DC-STAMP-deficient mice have been shown to exhibit moderate osteopetrosis, which was distinguished by TRAP+ mononuclear osteoclasts that could resorb bone inefficiently26, and mice that lacked Atp6v0d2 were shown to exhibit mild osteopetrosis owing to the absence of multinuclear TRAP+ osteoclasts, although they possessed mononuclear TRAP+ cells27. This evidence concerns the gene ACP5 and osteopetrosis.