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Bone and Mineral Metabolism

ORF08-05 - Real-World Effectiveness of Burosumab in Adults with X-Linked Hypophosphatemia (XLH): An Item-Level Analysis of the Western Ontario and McMaster Universities Osteoarthritis Index

Saturday, June 13, 2026
10:15 AM - 10:30 AM CT
Location: Room W179
Disclosure(s):
Erik A. Imel, MD: Amgen Inc.: Advisory Board (), Clinical Trial Investigator (); Calcilytix: Clinical Trial Investigator (); Kyowa Kirin: Advisory Board (), Clinical Trial Investigator (), Consultant (); Neurocrine: Advisory Board (), Clinical Trial Investigator (); UltraGenyx: Advisory Board (), Clinical Trial Investigator (), Consultant ()



Background: Clinical manifestations of X-linked hypophosphatemia (XLH) include pain, stiffness, fatigue, and muscle weakness that lead to progressive functional limitation and diminished quality of life. Treatment options for adults with XLH include burosumab, an anti-FGF23 antibody, or oral phosphate/active vitamin D (Pi/D). The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) has been used to assess disease burden and treatment response in adults with XLH. The XLH Disease Monitoring Program (DMP) collects real-world data on patients with XLH and assesses the long-term safety and effectiveness of burosumab. This analysis evaluated WOMAC item-level responses in participants enrolled in the XLH DMP.

Methods: Burosumab-naïve participants from 2 adult XLH DMP cohorts, those who initiated burosumab between baseline and the year 1 visit and those who reported Pi/D use at baseline and never subsequently received burosumab, were assessed separately by treatment. For each cohort, the proportion of participants reporting each WOMAC item-level response was summarized across baseline, year 1, and year 3 visits to determine change in patient disease burden across WOMAC domains (pain, physical function, stiffness) over time. The change in participant-reported responses over time for the 24 WOMAC items was modeled using a generalized estimating equation (GEE). Changes in each item response over time were assessed using Chi-Square statistics and corresponding P values from the GEE model for each cohort.

Results: 109 adults (burosumab, n=54; Pi/D, n=55; mean [SE] age: 39.7 [1.4] years) were included. Overall, burosumab participants achieved statistically significant changes over time in 71% (17/24) of WOMAC items across 3 domains (pain [4/5], physical function [11/17], stiffness [2/2]). Items with statistically significant changes over time included pain walking on flat surfaces and standing upright, stiffness after first waking up and after sitting/lying/resting, difficulty walking on flat surfaces, getting in/out of a car/bus, going shopping, and getting out of bed (all P< 0.005), pain going up/down stairs and sitting/lying down, and difficulty standing, bending to the floor, getting up from sitting, getting in/out of the bath, sitting, getting on/off the toilet, and doing light household chores (all P< 0.05). In contrast, no statistically significant changes were observed in any WOMAC items for the Pi/D cohort over time.

Conclusions: Burosumab in adults with XLH was associated with statistically significant item-level improvements across multiple WOMAC domains, with potential for positive impact on activities of daily living. Such findings were not observed on Pi/D. A future opportunity would be to determine clinically meaningful differences in WOMAC scores at the item level for adults with XLH, against which these results could be benchmarked.