Interestingly, one study analyzed the RANKL and OPG levels not only in the serum of patients with hemophilia, but also in the synovial tissue of hemophilic joints (66) and found that the serum levels of RANKL and OPG were lower than in healthy controls, whereas at the tissue level increased expression of RANK and RANKL and decreased expression of OPG were detected (66). The gene discussed is TNFRSF11B; the disease is hemophilia.