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Burosumab Therapy Shows Benefit in Children with X-Linked Hypophosphatemia

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X-linked hypophosphatemia (XLH) is a hereditary disorder that results in low levels of phosphorous in the blood due to the kidneys abnormally processing phosphate, resulting in hypophosphatemia, rickets and/or osteomalacia, and diminished growth. In children with XLH, treatment with burosumab improved renal tubular phosphate reabsorption, serum phosphorus levels, linear growth, and physical function, and reduced pain and the severity of rickets in an open-label, phase 2 clinical trial (NCT02163577).

In the study, 52 children (aged 5-12 years) with X-linked hypophosphatemia were randomly assigned 1:1 to subcutaneous burosumab every 2 weeks or every 4 weeks, with the dose adjusted to achieve a serum phosphorus level at the low end of the normal range. Among the key findings were the following:

  • Mean Thacher rickets severity total score decreased from 1.9 at baseline to 0.8 at week 40 with dosing every 2 weeks and from 1.7 at baseline to 1.1 at week 40 with dosing every 4 weeks, which persisted at week 64;
  • Mean serum phosphorus level increased after the first dose in both groups, and >50% of patients in both groups achieving levels within the normal range by week 6;
  • Renal tubular phosphate reabsorption increased from baseline in both groups;
  • Across both groups, the mean serum alkaline phosphatase level decreased from 459 U per liter at baseline to 369 U per liter at week 64;
  • Mean standing-height z score increased in both groups, with greater improvement seen at all time points with 2-week dosing than with 4-week dosing;
  • Physical ability improved and pain decreased.

Based on this and another study (NCT02750618), in April 2018, the FDA approved burosumab-twza (Crysvita) for the treatment of XLH in pediatric patients aged 1 year and older. It also approved its use in adult patients based on two other studies.

Read more about the study here.


Carpenter TO, Whyte MP, Imel EA, et al. Burosumab therapy in children with X-linked hypophosphatemia. N Engl J Med. 2018;378(21):1987-1998.

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