title: Comparison of two assays for fibroblast growth factor (FGF)-23.
abstract: FGF-23 was recently shown to be involved in the development of several hypophosphatemic diseases, including X-linked hypophosphatemic rickets/osteomalacia (XLH) and tumor-induced rickets/osteomalacia (TIO). FGF-23 is processed between Arg179 and Ser180, and only full-length FGF-23 was shown to cause hypophosphatemia. Two assays for FGF-23 have been reported. One assay detects only full-length FGF-23. In contrast, the C-terminal assay recognizes both full-length and processed C-terminal fragment of FGF-23. However, discrepant results concerning circulatory levels of FGF-23 in patients with TIO and XLH have been reported using these two assays. We simultaneously measured FGF-23 levels in 13 patients with adult-onset hypophosphatemic osteomalacia and 29 patients with XLH by these two assays. The full-length assay indicated that FGF-23 was above the upper limit of the reference range in all patients with osteomalacia and in 24 of 29 patients with XLH. However, the C-terminal assay in dicated that FGF-23 was within the reference range in 3 of 13 patients with osteomalacia and 16 of 29 patients with XLH. In addition, there was no correlation between FGF-23 levels measured by these assays in patients with XLH whose FGF-23 was within the reference range by C-terminal assay. These results indicate that FGF-23 within the reference range by C-terminal assay does not rule out an increase in full-length FGF-23. In addition, because FGF-23 was high in most of these hypophosphatemic patients, these results support the notion that FGF-23 plays a major role in the development of hypophosphatemia in patients with TIO and XLH.
authors.affiliation: Division of Nephrology and Endocrinology, Department of Internal Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan.
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Ito
authors.forename: Seiji
authors.initials: S
authors.lastname: Fukumoto
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yasuda
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Hasegawa
authors.forename: Fumi
authors.initials: F
authors.lastname: Takemoto
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Tajima
authors.forename: Kazushige
authors.initials: K
authors.lastname: Dobashi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Yamashita
authors.forename: Toshiro
authors.initials: T
authors.lastname: Fujita
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002675:Child, Preschool; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D006801:Humans; D007015:Hypophosphatemia, Familial / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications; D010018:Osteomalacia / Q000150:complications / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D012016:Reference Values
chemical_list: C000717427:FGF23 protein, human; D010446:Peptide Fragments; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23