Journal
BONE
Volume 60, Issue -, Pages 87-92Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.bone.2013.12.001
Keywords
Fibroblast growth factor 23; FGF23; X-linked hypophosphatemia; Iron; Phosphate
Categories
Funding
- Kyowa Hakko Kirin, Pharma Inc.
- Kyowa Hakim Kirin, Pharma Inc.
- National Institute of Arthritis and Musculoskeletal and Skin Diseases
- National Institute on Aging of the National Institutes of Health [K23AR057096, R01AR42228, P01AG18397, KL2RR025760]
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Background: Excess fibroblast growth factor 23 (FGF23) causes hypophosphatemia in autosomal dominant hypophosphatemic ricicets (ADHR) and X-linked hypophosphatemia (XLH). Iron status influences C-terminal FGF23 (incorporating fragments plus intact FGF23) in ADHR and healthy subjects, and intact FGF23 in ADHR. We hypothesized that in XLH serum iron would inversely correlate to C-terminal FGF23, but not to intact FGF23, mirroring the relationships in normal controls. Methods: Subjects included 25 untreated outpatients with XLH at a tertiary medical center and 158 healthy adult controls. Serum iron and plasma intact FGF23 and C-terminal FGF23 were measured in stored samples. Results: Intact FGF23 was greater than the control mean in 100% of XLH patients, and >2SD above the control mean in 88%, compared to 71% and 21% respectively for C-terminal FGF23. In XLH, iron correlated negatively to log-C-terminal FGF23 (r = -0.523, p <0.01), with a steeper slope than in controls (p <0.001). Iron was not related to log-intact FGF23 in either group. The log-ratio of intact FGF23 to C-terminal FGF23 was higher in XLH (0.00 +/- 0.44) than controls (-0.28 +/- 0.21, p < 0.01), and correlated positively to serum iron (controls r = 0.276, p < 0.001; XLH r = 0.428, p < 0.05), with a steeper slope in XLH (p < 0.01). Conclusion: Like controls, serum iron in XLH is inversely related to C-terminal FGF23 but not intact FGF23. XLH patients are more likely to have elevated intact FGF23 than C-terminal FGF23. The relationships of iron to FGF23 in XLH suggest that altered regulation of FGF23 cleaving may contribute to maintaining hypophosphatemia around an abnormal set-point. (C) 2013 Elsevier Inc. All rights reserved.
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