FGF23 and chronic kidney disease: In fact, a positive association between high serum levels of sclerostin and FGF23 has also been found in CKD and other bone disorders related to abnormalities in mineral metabolism [14,75], and inactivating mutations in SOST, the gene encoding sclerostin, are associated with low levels of FGF23, overgrowth, and sclerosis of the skeleton [76].