Kyowa Kirin publishes three-year real-world XLH data in JBMR
Kyowa Kirin has announced the publication of three-year interim findings from its XLH Disease Monitoring Program (DMP) in the Journal of Bone and Mineral Research, offering a rare longitudinal comparison of burosumab (CRYSVITA) against the conventional combination of oral phosphate and active vitamin D in adults with X-linked hypophosphatemia (XLH).
The analysis drew on data from 109 adults enrolled in the DMP: 54 receiving burosumab and 55 receiving oral phosphate and active vitamin D (Pi/D). Outcomes measured included serum phosphate levels and patient-reported pain, stiffness, and physical function at years one and three. The DMP is a prospective, ten-year observational study spanning the US, Canada, and Latin America, and is run with input from clinical experts, patient advocates from the XLH Network, and representatives from both Kyowa Kirin and Ultragenyx Pharmaceutical.
Why this publication matters
No randomised controlled trial has directly compared burosumab with Pi/D in adults with XLH, making observational data of this kind an important, if imperfect, surrogate. Burosumab is a recombinant fully human monoclonal IgG1 antibody that binds and inhibits fibroblast growth factor 23 (FGF23), the protein responsible for excessive phosphorus loss in XLH. The conventional Pi/D regimen, by contrast, supplements phosphate and activates vitamin D without targeting the underlying FGF23-driven mechanism. Crucially, the two approaches cannot be used together: concurrent use is a contraindication for burosumab due to the risk of hyperphosphatemia.
Lead author Steven W. Ing, Professor of Clinical Medicine at The Ohio State University Wexner Medical Center, said real-world evidence in rare diseases like XLH is "invaluable, helping to deepen our understanding of the patient experience and treatment outcomes beyond clinical trials," and that the findings "can help inform clinical decision-making and the ongoing evolution of care."
The publication does not report headline efficacy figures in the press release, meaning the full comparative results on serum phosphate normalisation and patient-reported outcomes remain in the journal article itself. Clinicians and payers will need to consult the primary paper to assess the magnitude and durability of any observed differences between the two treatment arms.
Market and competitive context
XLH is a rare disease with an estimated prevalence of around one in 20,000, and the adult treatment population has historically been managed on Pi/D due to familiarity and cost. Burosumab, approved by the FDA for XLH in patients aged six months and older, commands a substantially higher price point, and real-world comparative data carries weight with health technology assessment bodies such as NICE in the UK and comparable agencies in Europe and Japan.
Kyowa Kirin is building a broader evidence platform around burosumab: alongside the DMP, the company is running the International XLH Registry in Europe and the SUNFLOWER study in Japan and South Korea. That multi-registry strategy signals an ambition to support reimbursement and formulary decisions across multiple markets, where payer pressure on high-cost rare-disease biologics continues to intensify.
The XLH space remains relatively concentrated, with burosumab as the only approved FGF23-targeting therapy. However, academic groups and smaller biotechs have explored alternative FGF23 pathway interventions, and longer-term, gene therapy approaches that could address the underlying PHEX mutation represent a potential future disruptor. For now, the three-year DMP data reinforces Kyowa Kirin's position as the evidence leader in adult XLH, though independent peer scrutiny of the observational methodology will be essential before the findings carry full clinical weight.