Article Dans Une Revue Journal of Clinical Endocrinology and Metabolism Année : 2025

Challenges in Estimating Renal Function in X-linked Hypophosphatemia because of formula Overestimation and FGF23 Effects

Mélanie Alice Legrand
  • Fonction : Auteur
Justine Bacchetta

Résumé

Abstract Introduction In X-linked Hypophosphatemia (XLH), phosphate and vitamin D analogs increase the risk of nephrocalcinosis and renal impairment. Kidney function assessment is challenging, as creatinine-based eGFR may overestimate GFR due to reduced muscle mass. Cystatin C may be alternatively used. Moreover, fibroblast growth factor 23 (FGF23) has been suggested to potentially impact GFR, leading to hyperfiltration and complicating kidney function assessment. Methods We conducted a single-center retrospective study on XLH adults to compare eGFR formulas (CKD-EPIcreat, CKD-EPIcyst) with true measured GFR (mGFR). Bias, precision and accuracy were calculated. In a subgroup, mGFR changes after burosumab initiation were assessed. Finally, we analyzed FGF23/GFR relationship in a pediatric cohort in whom FGF23 is also hypersecreted (fibrous dysplasia) to support our hypothesis that FGF23 leads to hyperfiltration. Results We included 20 patients (17 females, median age 35 years). None had nephrocalcinosis or hypercalciuria, but eight had secondary hyperparathyroidism. Median mGFR was 90 (85–107) mL/min/1.73m², significantly lower than CKD-EPIcreat [125 (114–121)] and CKD-EPIcyst [103 (118)] (respectively p<0.0001 and p=0.01). Bias was significantly greater with CKD-EPIcreat [-22 (-29; -13)] than CKD-EPIcyst [-13 (-19; -4)], with lower accuracy (25% vs. 93%). In five XLH patients, mGFR decreased from 98 to 84 mL/min/1.73m² after burosumab introduction. FGF23 moderately correlated with eGFR in 14 fibrous dysplasia patients (R=0.62, p=0.02). Conclusions eGFR overestimates GFR in XLH, increasing CKD misclassification risk. Annual cystatin C measurement is recommended if CKD is suspected. FGF23 impact on GFR should also be considered in burosumab-treated patients.

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Dates et versions

hal-05267825 , version 1 (18-09-2025)

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Sandrine Lemoine, Aurélie de Mul, Kevin Perge, Laurence Derain-Dubourg, Roland Chapurlat, et al.. Challenges in Estimating Renal Function in X-linked Hypophosphatemia because of formula Overestimation and FGF23 Effects. Journal of Clinical Endocrinology and Metabolism, 2025, ⟨10.1210/clinem/dgaf459⟩. ⟨hal-05267825⟩
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