IMPE Abstracts

Introduction: X-linked hypophosphatemia (XLH) is a rare hereditary condition of phosphate wasting leading to rickets and short stature in childhood, additional adult manifestations, and lifelong stiffness, chronic pain, muscle weakness, and fatigue.

Methods: UX023-CL401 (NCT03651505) is a prospective, multinational, multicenter, longitudinal, disease monitoring program (DMP) that aims to characterize the clinical, radiographic, and biochemical features of XLH in adults and children with a planned 10-year duration. The goal of this subanalysis was to describe the pediatric Latin American (LATAM) XLH population participating in a long-term clinical monitoring program to better understand the disease characteristics and management strategies in this region as of March 2022.

Results: As of March 2022, 332 children (<18 years) participated in the DMP study, 74 of which were from LATAM. Children were from Brazil (24/74, 32.4%), Chile (16/74, 21.6%), Argentina (28/74, 37.8%), and Colombia (6/74, 8.1%). The mean (SD) age at enrollment was 8.8 (4.7) years, with a mean (SD) time since diagnosis of 6.5 (4.8) years. At DMP baseline, mean (SD) serum phosphate was 2.8 (0.5) mg/dL, serum alkaline phosphatase was 446.5 (181.2) U/L, serum 1,25 dihydroxyvitamin D was 49.0 (18.0) pg/mL, and serum intact parathyroid hormone was 58.9 (40.3) pg/mL. The most commonly reported symptoms of XLH included bowing of the legs (58/74, 78.4%), intoeing (21/74, 28.4%), craniosynostosis, and knock knees (both 17/74, 23.0%). At baseline, the mean (SD) Rickets Severity Score (on a scale from 1 to 10) was 3.0 (1.9), with Knee and Wrist scores of 1.5 (1.0) and 1.3 (1.1), respectively. Most (72/74) LATAM children (97.3%) had ever been treated with phosphate and active Vitamin D therapy. As of March 2022, 12/74 LATAM children (16.2%) had received burosumab therapy. Nineteen of 74 LATAM children (25.7%) receive pain medication to manage their disease, the most common of which was analgesics in 18/74 children (24.3%). At DMP Baseline, the mean (SD) number of school days within the last year were 2.8 (13.3) for XLH-related symptoms and 11.0 (24.1) for disease-related clinical care. Assistive devices were used by 3/74 LATAM children (4.1%) at DMP Baseline.

Conclusions: Overall, XLH patient characteristics in LATAM of the DMP highlight the need for improved access to advanced medical therapy. The 10-year DMP study of patients with XLH will increase our understanding of the disease and its response to various treatment regimens as additional data are collected.