Levels and dynamic changes of serum fibroblast growth factor 23 in hypophosphatemic rickets/osteomalacia.

BACKGROUND: Hypophosphatemic rickets/osteomalacia is a group of diseases characterised by defective mineralization of bone due to hypophosphatemia and low 1,25-dihydroxy vitamin D. To explore the role of fibroblast growth factor 23 (FGF-23) in the regulation of phosphate homeostasis, we measured the circulating concentrations of this growth factor in healthy individuals and in patients with hypophosphatemic rickets/osteomalacia. METHODS: Nineteen patients with hypophosphatemic rickets/osteomalacia were included in hypophosphatemic group (HP, 12 female and 7 male, mean age was 30 years), and 19 healthy age-matched individuals served as the control group. Full length FGF-23 fragments were measured by two-site enzyme-linked immunosorbent assay. RESULTS: Mean FGF-23 concentrations were significantly higher in the HP group ((87.4 +/- 43.6) pg/ml) compared with the control group ((19.2 +/- 6.16) pg/ml; P < 0.001). In 1 patient with tumour-induced osteomalacia, serum FGF-23 concentrations were 84.1 pg/ml; these concentrations were normalized 2 hours after a hemangiopericytoma resection (7.8 pg/ml). Subsequently, serum 1,25(OH)(2) vitamin D3 concentrations significantly increased from 21.3 pg/ml to 89.3 pg/ml, and serum phosphorus levels were normalized. CONCLUSIONS: Serum FGF-23 concentrations were markedly elevated in patients with hypophosphatemic rickets. FGF-23 plays an important role in the pathogenesis of hypophosphatemic rickets/osteomalacia.