FGF23 was initially identified in studies on autosomal dominant hypophosphatemic rickets (ADHR), in which mutations in the FGF23 gene lead to excessive serum FGF23 concentration by preventing cleavage of the active intact FGF23 (iFGF23) into inactive N-terminal and C-terminal FGF23 (cFGF23). Here, FGF23 is linked to autosomal dominant hypophosphatemic rickets.