FGF23 and chronic kidney disease: To test whether genetic ablation of Fgf23 would rescue the suppression of TNAP activity and pyrophosphate accumulation in CKD mice, we performed 5/6-Nx in Fgf23−/−/VDRΔ/Δ (Fgf23/VDR) compound mutants, which are characterized by concomitant Fgf23 deficiency and lack of a functioning vitamin D receptor (VDRΔ/Δ).