FGF23 and hypophosphatemia: PHEX regulates FGF23 expression whereas high FGF23 concentration in serum results in hypophosphatemia and low concentration of 1,25-dihydroxyvitamin D by damaging renal reabsorption of phosphate and 1a-hydroxylase activity, as well as increasing the activity of renal 24-hydroxylase (Baroncelli and Mora, 2021).