One of the key differences between Dmp1−/− and kl/kl mice is the Pi level: the former shows hypophosphatemia due to an abnormal increase of FGF23 that leads to Pi waste [8] and the latter is associated with hyperphosphatemia, which is due to a failure of FGF23 to remove extra Pi in the absence of Klotho, the key co-receptor [20], [35]. The gene discussed is KL; the disease is hyperphosphatemia.