Linear growth of children with X-linked hypophosphatemia treated with Burosumab: a real-life observational study

Abstract

Abstract Purpose To assess the long-term efficacy of burosumab for paediatric patients with X-linked hypophosphatemia, focusing on linear growth. Methods This multi-center retrospective study included 35 paediatric patients who began treatment with burosumab between January 2018 and January 2021. We collected clinical data, anthropometric measurements, laboratory results and rickets severity score (RSS), from two years prior to treatment initiation and up to four years after. Results Burosumab was initiated at a mean age of 7.5 ± 4.4 years (range 0.6–15.9), with a mean initial dose of 0.8 ± 0.3 mg/kg, which was subsequently increased to 1.1 ± 0.4 mg/kg. The patients were followed for 2.9 ± 1.4 years (range 1–4) after initiating burosumab. Serum phosphorus levels increased from 2.7 ± 0.8 mg/dl at burosumab initiation to 3.4 ± 0.6 mg/dl after three months, and remained stable (p < 0.001). Total reabsorption of phosphorus increased from 82.0 ± 6.8% to 90.1 ± 5.3% after 12 months of treatment (p = 0.041). The RSS improved from 1.7 ± 1.0 at burosumab initiation to 0.5 ± 0.6 and 0.3 ± 0.6 after 12 and 24 months, respectively (p < 0.001). Both height z-score and weight z-score improved from burosumab initiation to the end of the study: from − 2.07 ± 1.05 to -1.72 ± 1.04 (p < 0.001), and from − 0.51 ± 1.12 to -0.11 ± 1.29 (p < 0.001), respectively. Eight children received growth hormone combined with burosumab treatment. Height z-score improved among those who received growth hormone (from − 2.33 ± 1.12 to -1.94 ± 1.24, p = 0.042) and among those who did not (from − 2.01 ± 1.01 to -1.66 ± 1.01, p = 0.001). Conclusion Burosumab treatment in a real-life setting improved phosphate homeostasis and rickets severity, and enhanced linear growth.