Burosumab Improves Symptom Relief in Genetic Rickets

A study comparing the efficacy of burosumab with conventional treatment—oral phosphate and active vitamin D—found that burosumab, which blocks FGF23, was significantly more effective in alleviating symptoms.

A study comparing burosumab (Crysvita) with conventional treatment for a rare musculoskeletal disease found that burosumab was significantly more effective in alleviating symptoms of the disease.

X-linked hypophosphatemia (XLH) is a rare phosphate-wasting genetic disease that affects 1 in every 20,000 people and causes rickets and osteomalacia, or softening of the bone. The disease is characterized by elevated serum concentrations of fibroblast growth factor 23, rickets, bowed legs, and growth impairment. In April 2018, the FDA approved burosumab for the treatment XLH in adults and children aged 1 year or older.

“This is the first study comparing burosumab head-to-head with conventional therapy,” Erik Imel, MD, associate professor of medicine at Indiana University School of Medicine, said in a statement. “We now know the magnitude of benefit from burosumab over the prior approach with conventional therapy. This information is critical for doctors to make treatment decisions for patients with XLH.”

Between August 3, 2016, and May 8, 2017, the researchers recruited 61 children between the ages of 1 and 12 years at 16 centers around the globe, including in the United States, Canada, the United Kingdom, Sweden, Australia, Japan, and Korea. A total of 32 patients received conventional therapy—oral phosphate and active vitamin D—while 29 received burosumab 0.8 mg/kg every 2 weeks.

Observed for a total of 64 weeks, 72% of children who received burosumab achieved significant relief of rickets by 40 weeks of treatment, compared with just 6% of children receiving conventional therapy. The treatment also led to greater improvements in leg deformities, growth, distance walked in a 6-minute test, and serum phosphorus and active vitamin D levels.

Treatment-emergent adverse events considered possibly, probably, or definitely related to treatment were more frequently observed among patients receiving burosumab compared with conventional treatment (59% vs 22%). There were 3 serious adverse events that occurred in each group, all of which were unrelated to treatment.

The researchers noted that they plan on continuing to study the long-term effects of burosumab, including the effect on height outcomes as an adult and whether the treatment will decrease the need for surgeries to correct bowed legs.


Imel E, Glorieux F, Whyte M, et al. Burosumab versus conventional therapy in children with X-linked hypophosphataemia: a randomised, active-controlled, open-label, phase 3 trial [published online May 16, 2019]. Lancet. doi: 10.1016/S0140-6736(19)30654-3.

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