Non-nutritional rickets: Approach, precision medicine, and outcomes

Figure 5 Actions of fibroblast growth factor 23 in phosphate homeostasis. Schematic showing regulation of phosphate and calcitriol (1,25-dihydroxyvitamin D) by fibroblast growth factor 23 (FGF-23). Increased serum phosphate and calcitriol stimulate FGF-23 secretion. FGF-23 acts on the renal proximal tubule to inhibit sodium-phosphate cotransporters NaPi-IIa (solute carrier family 34 member 1) and NaPi-IIc (solute carrier family 34 member 3), reducing phosphate reabsorption and lowering serum phosphate. It also suppresses renal 1α-hydroxylase (cytochrome P450 family 27 subfamily B member 1) and stimulates 24-hydroxylase (cytochrome P450 family 24 subfamily A member 1), decreasing calcitriol levels and intestinal phosphate absorption. Parathyroid hormone shows bidirectional interaction with FGF-23 in a negative feedback loop to maintain phosphate and calcitriol homeostasis.