KL and hypogonadism: The lack of FGF23 or Klotho causes a premature aging phenotype, such as hypogonadism, premature thymic involution, ectopic calcification, dermal atrophy, pulmonary emphysema, neurodegeneration, hearing loss and vascular calcifications.(2-5) There is some evidence to support this aging phenotype based on hyperphosphatemia.(6) In chronic kidney disease (CKD) and in the aging kidney, FGF23 serum level rises to control hyperphosphatemia via the FGF23-Klotho-vitamin D-PTH axis.