Serum phosphate concentration value is controlled by the kidney, which adapts 
phosphate reabsorption in the proximal tubule to the needs of the body and 
regulates intestine absorption of phosphate and calcium through calcitriol 
synthesis. Fibroblast Growth Factor 23 (FGF23) is a hormone that controls 
sodium-phosphate transporter and 1-alpha 25(OH) vitamin D hydroxylase expression 
in the renal proximal tubule. FGF23 is synthesized by bone cells in response to 
an increase in serum phosphate or calcitriol concentrations. The binding of 
FGF23 to a FGF receptor requires a protein named Klotho that is expressed in the 
kidney in the distal but not in the proximal tubule. The mechanism by which 
FGF23 controls proximal tubule function remains to be established. The 
alteration of the FGF23-Klotho axis in animal models and various human disorders 
is associated with abnormal control of body phosphate content confirming the 
major role played by these protein in phosphate homeostasis. This review details 
FGF23 and Klotho functions in normal conditions and in genetics or acquired 
disorders.