FGF23 and hyperphosphatemia: Disorders involving FGF23 lead to hyperphosphatemia due to increased renal tubular phosphate reabsorption, while serum calcium levels and renal function remain unaffected.3 Underlying mutations are found in the FGF23 gene, the KL gene encoding Klotho, an essential co‐receptor for FGF23 signaling, and most commonly in the GALNT3 gene.