SUN-749 Impact of Treatment with Burosumab versus Conventional Therapy on Patient-Important Outcomes in Adult X-Linked Hypophosphatemia: A Retrospective and Prospective Cohort Study

Abstract Disclosure: D.S. Ali: None. A. Kubba: None. M.H. Alabdely: None. R. Alnajimi: None. A.A. Alraddadi: None. E. Morgante: None. M. Brandi: Takeda, Eli Lilly & Company, Calcilytix, Kyowa Kirin, UCB, Abiogen, Alexion, Amolyt, Amorphical, Bruno Farmaceutici, CoGeDi, Echolight. A.A. Khan: Takeda, Amgen Inc, Alexion, Ascendis, Amolyt, Calcilytix.. Background: X-linked hypophosphatemia (XLH) is a rare inherited disorder affecting BONE AND MINERAL METABOLISM, causing osteomalacia, and other non-skeletal complications in adults. Historically, XLH has been managed with conventional therapy (CT) consisting of phosphate salts and active vitamin D. However, the advent of burosumab, offers a novel treatment pathway. To date, there is limited evidence on the comparative effectiveness of burosumab versus CT on patient-important outcomes in adults including pain, fatigue, quality of life (QoL), and physical function. Methods: We retrospectively reviewed charts of all patients with XLH, confirmed by DNA analysis, at our tertiary referral center in Canada. Phone interviews assessed pain and stiffness using the BPI-SF and WOMAC scales in individuals on burosumab versus CT. Higher BPI-SF scores indicate greater pain severity and life interference, while higher WOMAC scores reflect increased pain, stiffness, and functional limitation. Biochemical outcomes were compared between groups at two time points: 6 months before starting burosumab and 12-24 months after. Results: We included 16 patients (12 on burosumab, 4 on CT) with a mean (SD) age of 42.3 (18) years and BMI of 28.7 (5.6) kg/m². Half of the patients are living with obesity (BMI>30). The mean duration of burosumab use was 3 years. Of our patients, 50% of patients pathogenic PHEX variants, while 12.5% had variants of unknown significance. Over 12-24 months, ALP levels decreased by 8% in the burosumab group but increased by 23% in the CT group. The mean BPI pain score was lower with burosumab (3.5 vs. 4.9, p = 0.431). WOMAC physical function (27.3 vs. 44.3, p = 0.124) and total WOMAC scores (40.0 vs. 62.3, p = 0.122) were also lower with burosumab. Conclusions: Patients on burosumab had lower BPI pain, WOMAC physical function, and total WOMAC scores than those on CT, suggesting less pain, stiffness, and functional limitation. Lower WOMAC physical function scores for patients on burosumab indicate fewer difficulties completing daily tasks such as walking, sitting, and climbing stairs compared to CT. However, this was not statistically significant. More research with larger sample size is needed to confirm these findings and to further assess the impact of burosumab vs CT on outcomes important to adults with XLH. Presentation: Sunday, July 13, 2025