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On April 18, the FDA approved a listing application for the monoclonal antibody drug Burosumab (Crysvita) for the treatment of x-linked low phosphate-linked rickets (XLH) for children aged 1 and above and adults. Prior to that, Burosumab had received conditional approval from the European Union in February.

It is understood that Burosumab is the world’s first drug to be approved for treatment of XLH. It is also the third of seven drugs approved by the FDA in 2018.

Burosumab was developed by the Japanese pharmaceutical industry association and Kyowa Kirin and Ultragenyx, which is aimed at the development of fibroblast growth factor 23 (FGF23) in the recombinant completely humanized monoclonal IgG1 antibody.

FGF23 reduces the levels of phosphate and active vitamin D in serum by regulating phosphate excretion and the production of active vitamin D in the kidneys. The excessive activity of FGF23 caused the excessive consumption of phosphate, and Burosumab was combined with FGF23 to inhibit its biological activity.

In a study recruited 134 patients Ⅲ period in clinical, with 1:1 randomly assigned to 1 mg/kg dose burosumab or placebo, every 4 weeks, 24 weeks treatment. After 24 weeks, patients from both groups continued to open labelling tests, during which they received 1mg/kg of Burosumab every 4 weeks.

After 24 to 48 weeks of treatment, 84 percent of patients treated with Burosumab since the study began (n = 68) had achieved and maintained a higher level of serum phosphorus than normal (2.5mg /dL). 89% of patients who had been treated with Burosumab from placebo for 24 weeks (n = 66) achieved and maintained serum phosphorus levels above the normal threshold.

XLH is a rare genetic disorder and the most common low blood phosphate rickets, with one in 20,000 people affected by the disease. XLH is one of the few dominant genetic diseases in the X chromosome, although almost all of the x-linked diseases are recessive.

XLH in patients with kidney can not correctly deal with vitamin D and phosphorus, can cause low blood phosphorus levels, leading to the bone growth and development of children and adolescents is damaged, and bone mineralization is a problem in his life. But this is not caused by a kidney problem, but something in the blood circulation that causes the kidney to treat phosphorus as a waste, not enough to recycle it for bones and teeth.

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