FGF23 and hypophosphatemia: The lack of either FGF23 or αKlotho causes aberrant Ca/Pi and vitamin D metabolism, thus ensuring skeletal anomalies and ectopic calcification [59, 81, 82]. Fgf23−/−/Opn−/− double-knockout (DKO) mice mimic hyperphosphatemia in Fgf23−/− mice, but the severe osteoidosis in Fgf23−/− is markedly reduced [83]. Fgf23−/−/Slc34a1−/− DKO mice reverse hyper- to hypophosphatemia in keeping with hypomineralization in bone [84].