Injection of recombinant FGF23 into mice revealed two major actions of this factor: one action was the induction of renal phosphate wasting, resulting in hypophosphatemia, whereas the other was a distinct suppression of renal 1α‐hydroxylase (CYP27B1) mRNA expression.(3) Renal 1α‐hydroxylase is the key enzyme for vitamin D hormone (1,25(OH)2D) production. This evidence concerns the gene FGF23 and hypophosphatemia.