Twelve-year-old Maya used a wheelchair full time. Her legs couldn’t support her, and her bones broke easily. She had fibrous dysplasia — a rare condition where bone tissue grows abnormally. For years, doctors could only manage her pain. Then she started a new treatment. Within months, she stood. Then walked. Then took her first unaided steps in years.
She wasn’t alone. In a small but powerful study, every patient with fibrous dysplasia who took burosumab saw their phosphate levels return to normal. Many also saw bone pain markers drop. Some children gained mobility they’d never had before.
Fibrous dysplasia affects about 1 in 100,000 people. It happens when abnormal tissue replaces healthy bone. This weakens the skeleton, leading to fractures, deformities, and chronic pain. Most patients lose too much phosphate through their urine because their bones produce too much of a hormone called FGF23. Low phosphate makes it harder for bones to heal or grow strong.
Current treatments focus on symptoms. Doctors often prescribe phosphate supplements and vitamin D. But these don’t work well for everyone. They can cause stomach pain, kidney stones, or fail to raise phosphate enough. For years, patients and families have waited for a better option.
Now, a new approach is turning heads.
This doesn’t mean this treatment is available yet.
The hormone hijacking bone health
Think of your kidneys as a filter system. They clean your blood but keep important minerals like phosphate. FGF23 acts like a “release valve” — it tells the kidneys to dump phosphate into urine. In healthy people, this valve opens just enough.
In fibrous dysplasia, the valve is stuck open. Bone lesions pump out too much FGF23. The result? Phosphate levels drop. Bones can’t mineralize properly. They stay soft, weak, and prone to breaking.
Burosumab works like a plug for that leak. It blocks FGF23, so the kidneys hold onto more phosphate. The body gets what it needs to build stronger bone.
All patients hit the target
The study tested burosumab in 12 people — 7 children and 5 adults — all with fibrous dysplasia and low phosphate. They got injections every few weeks for a year.
Every single person reached the goal: phosphate levels in the mid to upper part of normal. Before treatment, most had severely low levels. After 48 weeks, the average phosphate level jumped from far below normal to right in the sweet spot.
Bone turnover also improved. Alkaline phosphatase — a marker of unhealthy bone activity — dropped by nearly half. High levels of this enzyme mean bones are breaking down faster than they should. Seeing it fall suggests the skeleton is stabilizing.
Gains beyond the lab tests
Lab numbers tell part of the story. The real wins showed up in daily life.
Two children went from using wheelchairs full time to walking on their own. One had never walked before. Others reported less pain, more energy, and better movement.
Kids also scored better on quality-of-life surveys. They felt stronger, played more, and were less limited by pain. Adults didn’t show clear trends in surveys, but their lab results still improved.
Doctors took bone scans and biopsies to check if the drug affected the lesions themselves. Good news: no signs that burosumab made the disease worse. The abnormal tissue didn’t grow faster or change in dangerous ways.
But the benefits aren’t guaranteed
Not everyone saw dramatic changes. Some patients felt better but didn’t gain new physical abilities. And while phosphate levels normalized in all, we don’t yet know how long the effects last.
Experts say this is a strong signal, not a final answer. “This drug targets the root problem — phosphate loss — not the bone lesions themselves,” said one researcher involved. “It won’t erase the disease, but it may stop some of the damage.”
For families, that could mean fewer fractures, less pain, and more independence.
What this means for patients
Right now, burosumab is approved only for other rare phosphate disorders, not fibrous dysplasia. That means access is limited. Insurance may not cover it.
But this study adds strong evidence that it should be considered. If larger trials confirm these results, approval could follow.
If you or your child has fibrous dysplasia and low phosphate, talk to your doctor. Ask if burosumab might be an option — through a clinical trial or special access program.
This was a small study — just 12 people. It wasn’t designed to prove long-term safety or major functional gains. Larger trials are needed.
Researchers plan to expand the study to more patients and follow them longer. They’ll look at whether early treatment prevents bone deformities. They’ll also study how long benefits last after stopping the drug.
Science moves slowly, especially for rare diseases. But for families who’ve waited decades, this is a meaningful step forward.
One day, a simple injection might help children with fibrous dysplasia stand, walk, and live with less pain. That day isn’t here yet — but it feels closer than ever.