For the past four decades, XLH has been treated by oral phosphate supplementation and calcitriol, which improves rickets and osteomalacia and the dental manifestations, but often does not resolve all aspects of the mineralization defects.
Mutated or absent PHEX protein/enzyme leads to a decreased serum phosphate level, which cause mineralization defects in the skeleton and teeth (osteomalacia/odontomalacia).
X-linked hypophosphatemia (XLH) caused by mutations in the Phex gene is the most common human inherited phosphate wasting disorder characterized by enhanced synthesis of fibroblast growth factor 23 (FGF23) in bone, renal phosphate wasting, 1,25(OH)<sub>2</sub>D<sub>3</sub> (1,25D) deficiency, rickets and osteomalacia.
XLH shows growth retardation, hypophosphatemia, osteomalacia, and defective renal phosphate reabsorption and metabolism of vitamin D. Most PHEX studies have focused on bone, and recently we identified osteopontin (OPN) as the first protein substrate for PHEX, demonstrating in the murine model of XLH (Hyp mice) an increase in OPN that contributes to the osteomalacia.
Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of certain mesenchymal tumors which secrete fibroblast growth factor-23 (FGF-23) responsible for causing features of hypophosphatemia and osteomalacia in these patients.
In adults with X-linked hypophosphatemia (XLH), excess FGF23 impairs renal phosphate reabsorption and suppresses production of 1,25-dihydroxyvitamin D, resulting in chronic hypophosphatemia and persistent osteomalacia.
X-linked hypophosphatemic rickets (XLHR) represents the most common form of genetic hypophosphatemia and causes rickets and osteomalacia in children because of increased FGF23 secretion and renal phosphate wasting.
Fibroblast Growth Factor 23 (FGF23) is a phosphaturic factor causing increased renal phosphate excretion as well as suppression of 1,25 (OH)<sub>2</sub>-vitamin D<sub>3.</sub> Highly elevated FGF23 can promote development of rickets and osteomalacia.
The same effects were seen in rodent bone models <i>in vitro</i>, in which we also detected formation of a sKL complex with FGF23-FGFR and decreased <i>Phex</i> (gene responsible for X-linked hypophosphatemic rickets (XLH)/osteomalacia) expression.
X-linked hypophosphataemia (XLH) is the most common heritable form of osteomalacia and rickets caused by a mutation in the phosphate regulating endopeptidase gene resulting in elevated serum fibroblast growth factor 23 (FGF23) and decreased renal phosphate reabsorption.
Phosphaturic mesenchymal tumor without osteomalacia: additional confirmation of the "nonphosphaturic" variant, with emphasis on the roles of FGF23 chromogenic in situ hybridization and FN1-FGFR1 fluorescence in situ hybridization.
X-linked hypophosphatemia (XLH) caused by mutations in the Phex gene is the most common human inherited phosphate wasting disorder characterized by enhanced synthesis of fibroblast growth factor 23 (FGF23) in bone, renal phosphate wasting, 1,25(OH)<sub>2</sub>D<sub>3</sub> (1,25D) deficiency, rickets and osteomalacia.
The high production of fibroblast growth factor 23 (FGF23) by the tumor is believed to be the causative factor responsible for the impaired renal tubular phosphate reabsorption, hypophosphatemia and osteomalacia.
Owing to the role of FGF23 in renal phosphate handling and vitamin D synthesis, TIO is characterized by decreased renal tubular reabsorption of phosphate, by hypophosphataemia and by low levels of active vitamin D. Chronic hypophosphataemia ultimately results in osteomalacia (that is, inadequate bone mineralization).
Loss of fibroblast growth factor-23 (FGF23) causes hyperphosphatemia, extraskeletal calcifications, and early mortality; excess FGF23 causes hypophosphatemia with rickets or osteomalacia.
Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome in which unregulated hypersecretion of fibroblast growth factor 23 (FGF23) by phosphaturic mesenchymal tumors (PMT) causes renal phosphate wasting, hypophosphatemia, and osteomalacia.
Sclerostin antibody (Scl-Ab) improves osteomalacia phenotype in dentin matrix protein 1(Dmp1) knockout mice with little impact on serum levels of phosphorus and FGF23.
Compared to Hyp mice, compound Hyp;Fgfr1Dmp1-cKO-null mice had significant improvement in rickets and osteomalacia in association with a decrease in serum FGF23 (3607 to 1099 pg/ml), an increase in serum phosphate (6.0 mg/dl to 9.3 mg/dl) and 1,25(OH)2D (121±23 to 192±34 pg/ml) levels, but only a 30% reduction in bone FGF23 mRNA expression.
Our finding of somatic activating RAS mutation in bone, the endogenous source of FGF23, provides the first evidence that elevated serum FGF23 levels, hypophosphatemia and osteomalacia are associated with pathologic Ras activation and may provide insight in the heretofore limited understanding of the regulation of FGF23.
Acquired syndromes of renal phosphate wasting, hypophosphatemia and osteomalacia (tumour-associated osteomalacia) can be due to the excessive synthesis or release of phosphaturic factors (FGF23, FGF-7, MEPE and sFRP4) from mesenchymal tumours.