Fig. 1.

a Renal phosphate wasting in X-linked hypophosphataemia. Reduced phosphate reabsorption in the proximal renal tubule is due to excessive FGF23, which stimulates the FGFR1c/α-klotho co-receptor complex at the basolateral membrane, resulting in reduced expression of sodium phosphate co-transporter NPT2a and NPT2c at the apical membrane. b Mechanism of action of burosumab: binding to excess FGF23 and thereby facilitating renal phosphate reabsorption from the proximal renal tubule. FGF23 fibroblast growth factor 23, FGFR1c fibroblast growth factor receptor 1c, NPT sodium-phosphate co-transporter