Real-world Data Support Effectiveness of Crysvita in Youngsters With XLH

One-year treatment with Crysvita (burosumab) reduced bone damage and increased phosphate levels in children and adolescents with X-linked hypophosphatemia (XLH), a study showed.

The study, “Real-life clinical study: 1-year of treatment with burosumab of children and adolescents affected with X-linked hypophosphatemia,” was presented online at the 2020 European Congress of Endocrinology (ECE).

XLH is characterized by elevated blood levels of the protein FGF23, which results in higher-than-normal amounts of phosphate in the urine. Phosphate is important for the development of bones and teeth, so lower levels in the blood can lead to rickets and other symptoms of XLH.

Crysvita — marketed by Kyowa Kirin and Ultragenyx Pharmaceutical — is an XLH treatment that works by blocking the activity of FGF23. In the U.S., Crysvita is approved to treat XLH from 6 months of age. In the European Union, the therapy is approved for children 1 and older, and adolescents with still-growing skeletons. The European Commission is currently reviewing a label update to expand Crysvita’s use to older adolescents and adults.

In the ECE presentation, researchers in France shared data about 57 children with XLH who were treated with Crysvita for one year. The group included 36 boys, 21 girls, and the average age was 9.1 years.

Ten participants were adolescents at least 13 years old (average 14.5 years). Notably, clinical trials of Crysvita in children have included patients ages 12 and younger.

The scientists explored the effect of Crysvita on XLH disease activity, which was measured primarily by imaging rickets-like lesions in the children’s knees with MRI scans. Results after a year of treatment showed lower disease activity, as lesions were, on average, about half as large as they had been prior to treatment.

The treatment significantly increased blood levels of phosphaste (0.73 to 1.19 mmol/L) and active vitamin D (25 to 79 picograms/ml). Crysvita also significantly decreased levels of alkaline phosphatase (418 to 299 units/L), an enzyme that can indicate liver or bone problems.

In addition, treatment improved six-minute walk test scores, which is a measurement of how far a child can walk in six minutes, relative to what is typical for children their age.

In contrast, Crysvita had no effect on age-adjusted height or the incidence of complications.

Adolescents tended to have higher levels of the phosphate-regulating protein parathyroid hormone (PTH) prior to treatment. However, these levels decreased substantially after a year on Crysvita, a finding the researchers described as “noteworthy.”

They also said that adolescents with hyperparathyroidism — a condition characterized by high PTH levels — tended to take longer to attain normalized phosphate levels.

“Our findings on efficacy and safety of burosumab [Crysvita] confirm those of clinical trials,” the scientists concluded, adding that Crysvita treatment “leads to healing of rickets, reduction of disease activity and improvement of physical function.”