FGF23 and X-linked dominant hypophosphatemic rickets: In this regard, there is a clear connection between FGF23 and NaPi-IIa and NaPi-IIc phosphate channels, as it has been shown that direct administration of recombinant FGF23 reduces the renal expression of NaPi-IIa in Hyp mice and in patients with XLH, while renal expression of NaPi-IIa and/or NaPi-IIc is downregulated in mice with high levels of FGF23 [6,12,16,49].