ECE2015 Eposter Presentations Calcium and Vitamin D metabolism (96 abstracts)
Acquired FGF23 resistance: the primacy of parathyroid hormone over fibroblast growth factor 23 in renal phosphorus handling
Malachi McKenna 1, , Sinead Kinsella 1 , Michelle Morrin 1 , Melissa Sloman 3 , Ahad Abdalla 1 , Myra O’Keane 1 , Barbara Murray 1 , John Holian 1, , Alan Watson 1, & Mark Kilbane 1
1St Vincent’s University Hospital, Dublin, Ireland; 2University College Dublin, Dublin, Ireland; 3Royal Devon and Exeter NHS Foundation Trust, Exeter, UK.
Introduction: Fibroblast growth factor 23 (FGF23) excess is the cause of chronic hypophosphatemia in rare conditions such as X-linked hypophosphataemic rickets (XLHR) and tumour-induced osteomalacia (TIO), but animal studies indicate that the effect of FGF23 on serum phosphorus is dependent on the presence of parathyroid hormone (PTH). In this case series of rare disorders with abnormalities in renal phosphorus handling, we sought to explore the relative roles of PTH and FGF23 on renal handling of phosphorus.
Methods: We studied 16 patients with congenital hypophosphatemia (of whom two were hypoparathyroid post total parathyroidectomy), two patients with TIO, one patient with hypophosphataemic bone disease due to congenital renal tubular acidosis, and three patients with hypoparathyroidism (HP). We performed genetic mutation analysis, and we measured FGF23, PTH, renal phosphorus threshold (TmP/GFR), ionised calcium, 25-hydroxyvitamin D (25OHD), and a panel of bone turnover markers (BTMs). We also studied 30 patients with chronic kidney disease (CKD) who had estimated glomerular filtration (eGFR) stages 3–5.
Results: Patients with congenital hypophosphatemia and TIO had low TmP/GFR and varying degrees of FGF23 excess. The patient with hypophosphatemia and renal tubular acidosis had the lowest FGF23 and the three patients with HP had low PTH, elevated FGF23, but high TmP/GFR. The two patients with congenital hypophosphatemia and hypoparathyroidism had normal TmP/GFR despite having marked elevation in both C-terminal and intact FGF23. Both patients had CKD, but FGF23 was still about tenfold higher than expected for level of eGFR.
Conclusions: While FGF23 is a determinant of TmP/GFR in congenital and acquired disorders of dysregulated FGF23 production, the full effect of FGF23 on TmP/GFR is dependent on PTH secretion. FGF23 resistance is extant when PTH is absent.
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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