FGF23 and hyperphosphatemia: In the absence of the suppressive effect of FGF23 signalling on renal 1α–hydroxylase, the normally tight regulation of this enzyme fails, and leads to excessive, unregulated production of 1,25(OH)2D. The subsequent intoxication with 1,25(OH)2D causes hypercalcemia and hyperphosphatemia, which in turn leads to soft tissue calcifications and early lethality.