ESPE Abstracts

Objectives: X-linked hypophosphataemia (XLH) is a rare, hereditary phosphate-wasting disorder characterised by excessive activity of fibroblast growth factor 23. The International XLH Registry (NCT03193476) (initiated in August 2017, target 1,200 children and adults with XLH, running for 10 years) will provide information on the natural history of XLH and impact of treatment on patient outcomes. This report summarises baseline data from the first interim analysis from paediatric participants (age <18y), according to the treatments they were receiving at study entry.

Methods: At the time of analysis (Last Patient In: 30/11/2020; Database Lock: 29/03/2021), participants diagnosed with XLH were enrolled from 81 hospital sites in 16 countries. Baseline parameters included demographics, clinical presentation data, and medical and treatment history.

Results: Overall, 360 children were included in this interim analysis; 61.7% female. Treatment data at entry were available for the majority of participants (281/360; 78.1%): 58.7% were receiving burosumab (BUR) (165/281); 40.6% conventional therapy (CT) (oral phosphate and active vitamin D) (114/281); 0.7% reported no treatment (2/281). Age distribution of children according to treatment at entry: BUR (n=165) : n=0, <1y; n=31, 1–<5y; n=78, 5–<12y; n=56, 12–<18y; mean (SD) age 9.60y (4.20); CT (n=114) : n=5, <1y; n=23, 1–<5y; n=45, 5–<12y; n=41 12–<18y; mean (SD) age 9.34y (5.18). Mean (SD) time from first symptoms to diagnosis 1.01y (1.87) in BUR group and 0.95y (1.90) in CT group. Retrospective XLH clinical data were available at entry for 115/165 children in BUR group and 81/114 in CT group. Craniosynostosis was reported in 27.0% (31/115) children in BUR group and 14.8% (12/81) children in CT group. In children with renal clinical conditions, nephrocalcinosis was reported in 100% (39/39) children in the BUR group and 100% (15/15) children in the CT group. In children with dental conditions, tooth abscess was reported in 80.4% (41/51) in the BUR group and 86.7% (26/30) in the CT group.

Conclusions: This is the largest data set of children with XLH collected to date. The mean time to diagnosis was 6–7 years; increased disease awareness of XLH may improve and shorten the diagnostic journey. Children receiving BUR at study entry tended to be slightly older than those receiving CT and reported more craniosynostosis. This may reflect triaging of children XLH with more severe symptoms to receive this new treatment modality. Authors acknowledge the contribution of all the International XLH Registry Steering Committee members.