FGF23 and vitamin D deficiency: Osteomalacia is mainly caused by vitamin D deficiency and renal calcium (Ca) or phosphate (P) wasting, which is characterized by an increased filtered P load due to hyperphosphatemia (excess excretion of P) or decreased proximal tubular P reabsorption through solute carrier family 34 member 1 (SLC34A1) by the phosphaturic action of parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF‐23).12