A Study to Describe the Lived Experience of XLH for Adolescents at End of Skeletal Growth

This an observational, prospective, European, multicentre, mixed methods study that will involve the integration of quantitative and qualitative data exploring the lived experience of burosumab-treated adolescents with XLH at the end of skeletal growth. The study will involve two observation periods around the confirmed date of end of skeletal growth (index date)

The purpose of this study is to describe the lived experience of XLH for adolescents who are being treated with burosumab at the end of skeletal growth, with a focus on adolescent reported symptoms, activity duration and intensity, and wider burden, and to describe change over time for those who continue and discontinue burosumab at the end of skeletal growth. The study will also explore the experiences of carers at the time the adolescent reaches the end of skeletal growth.

The key objectives of this study are to:

1. Describe the lived experience of adolescents with XLH who are being treated with burosumab within the 12 weeks prior to reaching the end of skeletal growth. 2. Describe the lived experience of adolescents with XLH during the 26 weeks immediately after the end of skeletal growth, overall and according to whether they continue or discontinue burosumab treatment. 3. Describe within-person changes in the lived experience of adolescents with XLH after reaching end of skeletal growth, in relation to their own pre-end of skeletal growth period. 4. Explore the supportive care needs and burden on carers at the time the adolescent with XLH reaches end of skeletal growth.