Fig. 1.
Simplified schematic outline of how FGF23 may exert physiological and pathological responses. Under physiological conditions, FGF23-mediated systemic regulation of phosphate homeostasis is a Klotho-dependent process. Under pathological conditions, however, an excessive amount of FGF23 may bind its receptors with low affinity without Klotho to exert non-specific effects that might influence organ functions.