FGF23 and congenital bilateral aplasia of vas deferens from CFTR mutation: The klotho (Kl–/–) and/or Fgf23 (Fgf23–/–) knockout mice exhibit many key aspects associated with human CAVD including, premature aging, kidney disease, increased serum phosphate levels (i.e., hyperphosphatemia), and increased osteogenic gene expression (7, 23, 24).