Discussion We have previously reported the presence of elevated FGF23 concentrations in Gambian children with a history of rickets-like bone deformities [7, 8] as determined by the C-terminal Immutopics Tariquidar ELISA assay. Albeit at a lesser prevalence, we have also reported elevated FGF23 concentrations in children from the local community [8]. It has been suggested that these measurements could be a reflection of the inactive C-terminal fragments detected by the Immutopics ELISA and therefore not a true reflection of the concentrations of biologically

functional intact FGF23 hormone. In order to explore this eventuality we used the same antibody as the C-terminal Immutopics ELISA kit in a western blot to determine which protein fragments were being detected by the ELISA. This confirmed detectable fragments in the

standard material but not in the Gambian samples. This suggests that the high FGF23 concentrations, as measured by the C-terminal Immutopics ELISA in Gambian children with and without bone deformities, are a reflection of circulating intact FGF23 protein rather than high levels of cleaved product. Furthermore, protein staining indicated that there were no proteins of low molecular selleck products weight in the plasma samples suggesting the absence of any type FGF23 fragments, not only C-terminal fragments. Limitations of this study include the small number of plasma samples available for the analysis. In conclusion, a difference in proportion of cleaved FGF23 hormone does not explain the presence of high FGF23 in Gambian children with rickets-like bone deformities and in children from the local community [8]. Acknowledgments The work was performed at MRC Human Nutrition Research, Cambridge, UK on samples collected at MRC Keneba, The Gambia and supported by the UK Medical Research Council [Unit Program

numbers U105960371, U105960399 and U123261351]. Fossariinae We would like to thank Immutopics for their antibody donation. Conflicts of interest None. Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. References 1. Liu S, Zhou J, Tang W, Jiang X, Rowe DW, Quarles DL (2006) Pathogenic role of FGF23 in Hyp mice. Am J Physiol Endocrinol Metab 291(1):E38–E49PubMedCrossRef 2. Burnett SAM, Gunawardene SC, Bringhurst RF, Jüppner H, Lee H, Finkelstein JS (2006) Regulation of c-terminal and intact FGF-23 by dietary phosphate in men and women. JBMR 21(8):1187–1196CrossRef 3. Nishi H, Nii-Kono T, Nakanishi S, Yamazaki Y, Tamashita T, Fukumoto S, Ikeda K, Fujimori A, Fukugawa M (2005) Intravenous calcitriol therapy increases serum concentrations of fibroblast growth factor-23 in dialysis patients with secondary hyperparathyroidism. Nephron Clin Pract 101:c94–c99PubMedCrossRef 4.