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Abstract: SA-PO470

Burosumab Improved Rickets and Clinical Outcomes Compared to Conventional Therapy in Children with XLH

Session Information

  • Pediatric Nephrology - II
    October 27, 2018 | Location: Exhibit Hall, San Diego Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical


  • Portale, Anthony A., University of California San Francisco, San Francisco, California, United States
  • Imel, Erik, Indiana University School of Medicine , Indianapolis, Indiana, United States
  • Munns, Craig, The Children''s Hospital at Westmead, Westmead, New South Wales, Australia
  • Ward, Leanne M., Children's Hospital of Eastern Ontario, University of Ottawa, Ottawa, Ontario, Canada
  • Whyte, Michael, Washington University School of Medicine, St. Louis, Missouri, United States
  • Simmons, Jill, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Padidela, Raja, Manchester University NHS Foundation Trust, Manchester, United Kingdom
  • Mao, Meng, Ultragenyx Pharmaceutical Inc., Novato, California, United States
  • Skrinar, Alison, Ultragenyx Pharmaceutical Inc., Novato, California, United States
  • San martin, Javier, Ultragenyx Pharmaceutical Inc., Novato, California, United States
  • Glorieux, Francis H., Shriners Hospital for Children-Canada, Montreal, Quebec, Canada

In children with X-linked hypophosphatemia (XLH), high circulating levels of FGF23 cause hypophosphatemia with consequent rickets, skeletal deformities, and growth impairment. Burosumab is an FDA-approved fully human monoclonal antibody against FGF23 for patients ≥1 year of age with XLH. Conventional therapy consists of multiple daily doses of oral phosphate and active vitamin D (Pi/D).


In the study CL301 (NCT02915705), 61 children with XLH (1-12 years old) were randomized (1:1) to receive subcutaneous burosumab starting at 0.8 mg/kg every 2 weeks (wk) or Pi/D as prescribed by the investigator. Eligibility criteria included a Total Rickets Severity Score (RSS) ≥2.0.


Burosumab showed significantly greater improvement than Pi/D in rickets as assessed by radiologists blinded to treatment using the radiographic global impression of change (RGI-C) at Wk 40 (primary endpoint). More subjects in the burosumab group had substantial healing (RGI-C ≥+2.0) at Wk 40, compared with the Pi/D group (21/29, 72% vs 2/32, 6%; odds ratio of healing 39.1, p<0.0001). Decreases in rickets severity assessed by RSS and alkaline phosphatase also were greater with burosumab. Increases in serum phosphorus were greater with burosumab than with Pi/D. Standing height Z-score increased from a baseline mean (SD) of -2.32 (1.17) to -2.12 (1.22) at Wk 40 for burosumab; and from -2.05 (0.87) to -1.97 (0.87) for Pi/D. Percent predicted distance walked increased with burosumab (Baseline to Wk 40: 62% to 72%) and was unchanged with Pi/D (76% to 75%). Adverse events of interest were higher in the burosumab group, but were mild to moderate in severity overall, with no discontinuations.


Burosumab resulted in significantly greater improvement in rickets and serum phosphorus than conventional therapy in 1-12 year-old children with XLH.

Summary of Efficacy in UX023-CL301
AssessmentPi/D (N = 32)Burosumab (N = 29)Difference, p-value
RGI-C Global Score at Week 40, LS Mean ± SE+0.77 ± 0.11+1.92 ± 0.111.14, p<0.0001
Total RSS, LS mean ± SE Change from Baseline to Week 40-0.71 ± 0.138-2.04 ± 0.145-1.34, p<0.0001
Alkaline Phosphatase, U/L, LS Mean ± SE Change from Baseline to Week 40-35 ± 19-131 ± 13-97, p<0.0001
Serum Phosphorus, mg/dL, LS Mean ± SE Change from Baseline to Week 40+0.20 ± 0.06+0.92 ± 0.080.71; p<0.0001
TmP/GFR, mg/dL, LS Mean ± SE Change from Baseline to Week 40-0.17 ± 0.08+1.16 ± 0.121.33, p<0.0001

Higher RGI-C and lower RSS = improvement; p-values from ANCOVA (Rickets) & GEE (ALP, TmP/GFR, and Pi).


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