FGF-23 (Fibroblast growth factor 23) is a regulator of phosphate homeostasis. It upregulates EGR1 expression in the presence of KLBy. Acts directly on the parathyroid to decrease PTH secretion. Regulates the vitamin-D metabolism. Negatively regulates osteoblast differentiation and matrix mineralization. Defects in FGF-23 are the cause of autosomal dominant hypophosphataemic rickets (ADHR) and of hyperphosphatemic familial tumoral calcinosis (HFTC).