A promising targeted therapy may offer new hope to children and adults living with fibrous dysplasia, a rare bone disorder that weakens bones and severely affects mobility. Researchers have reported that the drug burosumab significantly improved phosphate balance and physical function in patients suffering from the debilitating condition.
Fibrous dysplasia occurs when normal bone is gradually replaced with abnormal fibrous tissue, leading to fractures, bone deformities, chronic pain, and movement difficulties. In many patients, the disease causes excessive production of fibroblast growth factor-23 (FGF23), a hormone that triggers phosphate loss through the kidneys. Since phosphate is essential for healthy bone mineralization, long-term deficiency can worsen skeletal damage and disability.
The study was led by Alison M. Boyce and involved a phase 2 clinical trial evaluating burosumab, a monoclonal antibody designed to block FGF23 activity. The trial included 12 participants — seven children and five adults — all experiencing severe disease and low phosphate levels. Participants received treatment over 48 weeks while researchers monitored bone health, mobility, imaging findings, and patient-reported outcomes.
According to the findings published in the journal Bone Research, burosumab successfully restored phosphate levels into the normal range for all participants by the end of the study. Researchers also observed improvements in kidney phosphate retention and vitamin D activity, both important for maintaining bone strength.
One of the most striking outcomes was the improvement in mobility among pediatric patients. Several children experienced reduced fatigue and pain, while two severely affected participants showed dramatic progress. One child who previously depended on a wheelchair was able to walk independently after treatment, while another who had never walked alone managed to walk short distances with a walker.
Researchers noted that the therapy was generally well tolerated, with only mild side effects such as temporary increases in phosphate levels and minor injection-site reactions. Importantly, imaging scans found no evidence that the treatment accelerated abnormal bone growth, a major concern in therapies targeting FGF23 signaling.
The investigators believe the findings could influence treatment approaches for other disorders linked to phosphate imbalance. They also suggest that earlier intervention in children may help reduce long-term disability and improve quality of life for patients affected by rare skeletal diseases.
