Novel factors such as Klotho and Sclerostin, which are involved in the bone-kidney-parathyroid endocrine axis, have been identified recently. Klotho is a putative aging suppressor gene and its deficiency results in osteopenia, hyperphosphaturia, and calcification. Klotho is mainly expressed in the kidney but also in the parathyroid gland and acts as a FGF23 specific co-receptor mediating FGF23 participation in the bone-kidney-parathyroid endocrine axis as described above. Interestingly, secreted Klotho is also able to induce phosphaturia independently of FGF23 (15).