Serum phosphate and calcium levels. Serum phosphate and calcium levels in WT, klotho−/−, DKO+NPD, and DKO+HPD mice at 3, 6, and 9 wk of age. Serum phosphate (left panel) and calcium (right panel) levels are higher in klotho−/− mice when compared with WT mice at 3, 6, and 9 wk of age. In contrast to klotho−/− mice, serum phosphate levels are markedly reduced in DKO+NPD mice. Serum phosphate levels are significantly increased in DKO+HPD mice. Increased serum calcium levels are observed in normal-phosphate diet-fed klotho−/− and DKO+NPD mice compared with WT controls, but levels are slightly lower in DKO+HPD mice. *P < 0.05, **P < 0.01 vs. WT; ¶P < 0.01, ¶¶P < 0.001 vs. klotho−/−; #P < 0.05, ##P < 0.001 vs. DKO+NPD.