Effect of burosumab conversion on calciuria and nephrocalcinosis in children with XLH: A real-world cohort study

Background: Burosumab, a monoclonal antibody to fibroblast growth factor 23 (FGF23), is effective for X-linked hypophosphatemic rickets (XLH). Renal effects, particularly calciuria and nephrocalcinosis, remain incompletely characterized. Methods: In this retrospective cohort, 13 children with genetically confirmed XLH (7 females, 6 males; 0.6-16.3 years) were evaluated after conversion from conventional therapy to burosumab. Longitudinal changes in serum phosphate, TmP/GFR, TRP, 1,25(OH)₂D, intact parathyroid hormone (PTH), and urinary calcium/creatinine (Ca:Cr) were assessed. Hypercalciuria was defined using age-specific SI thresholds; Ca:Cr was also expressed as ×ULN (Ca:Cr divided by the age-specific upper limit). Results: < 0.05), whereas 1,25(OH)₂D did not. Conclusion: Burosumab improves phosphate homeostasis in children with XLH, but a minority may develop hypercalciuria and nephrocalcinosis, potentially linked to PTH suppression. Vigilant biochemical and ultrasound monitoring-particularly early after conversion-and consideration of prophylaxis in high-risk cases are advisable.