FGF23 and hypophosphatemia: Additionally, hypophosphatemia blunts the production of parathyroid hormone (PTH) [2] and fibroblast growth factor 23 (FGF23) [3], releasing the inhibitory effect of both hormones on renal phosphate cotransporters (NaPi-IIa, NaPi-IIc and PiT-2), thus enhancing renal reabsorption of phosphate.