Circulating levels of soluble klotho and FGF23 in X-linked hypophosphatemia: circadian variance, effects of treatment, and relationship to parathyroid status.

Context: Circulating fibroblast growth factor (FGF)-23 is variably elevated in individuals with X-linked hypophosphatemia (XLH), and klotho has recently been shown to effect renal phosphate handling, yet limited data are available on circulating FGF23 and klotho in XLH.

Objective: The objective of the study was to characterize circulating FGF23 and klotho in XLH.

Design: Children and adults with XLH withheld medication for 14 d.