Phosphate homeostasis is maintained by regulating intake, intestinal absorption, bone deposition and resorption, and renal excretion of phosphate. The central molecule in the control of phosphate excretion from the kidney is the sodium/phosphate cotransporter NPT1 (SLC17A1; MIM 182308), which is located in the renal proximal tubule. NPT1 uses the transmembrane electrochemical potential gradient of sodium to transport phosphate across the cell membrane. SLC17A4 is a similar sodium/phosphate cotransporter in the intestinal mucosa that plays an important role in the absorption of phosphate from the intestine (summary by Shibui et al., 1999 [PubMed 10319585]).[supplied by OMIM, Feb 2011].