CD9 and osteoporosis: The fact that our data show a strong linkage between the presence of integrin α2β1 with CD9 in differentiating OCs, would provide a rationale to extent the polymorphism studies of ITGA2 on platelets to patients with dysfunctional bone turnover and to correlate the different ITGA2 alleles to the risk of osteoporosis or osteopetrosis in aged patients.