With or without the kidney: the role of FGF23 in CKD

The systemic balance of phosphate is maintained mainly by three organs, i.e. the intestine, kidney and bone. Several factors including parathyroid hormone (PTH) and vitamin D play a critical role in this system. Fibroblast growth factor 23 (FGF23) is a recently identified phosphatonin which also is implicated [1,2]. It has been demonstrated in several diseases that excessive activity of FGF23 resulted in hypophosphataemia, low plasma 1,25-dihydroxyvitamin D (1,25D) levels and osteomalacia [3–5]. In animals, the administration of recombinant FGF23 led to the same results [6]. Furthermore, overexpression of FGF23 led to phosphate wasting [7] and rickets, while ablation of this gene led to hyperphosphatemia and high circulating 1,25D levels [8].