OBJECTIVES: A European, prospective, multi-centre, mixed-methods observational study is in development to investigate treatment transition and disease experience in adolescents with X-Linked Hypophosphatemia (XLH), a rare, genetic life-long phosphate-wasting disorder. To ensure robustness, feasibility and patient-centricity of study design, a UK patient-public involvement (PPI) project was undertaken.

METHODS: During June 2020, four adolescents (14-18 years), recruited via patient group XLH UK, underwent 1:1 semi-structured 60-minute telephone interviews (following informed consent). Participants described their experience of known symptoms and impacts of XLH identified from the literature and burosumab trials (pain, stiffness, mobility and physical function, tiredness/fatigue, sleep, emotional wellbeing) and then prioritised their importance for measurement. The acceptability of proposed methods for data capture (e.g. use of wearables, smartphone app), recruitment, and retention of participants was also discussed. Responses were summarised narratively in MS Excel to aid future study design.

RESULTS: The interference of pain, stiffness and tiredness/fatigue on daily physical activities were identified as key endpoints, alongside modifications to daily activities and socialising for symptom management. Mild symptoms were reported by most participants, either due to effective treatment or reduced activity during COVID-19. One participant was more concerned with emotional wellbeing, relating to self-confidence, and favoured its measurement in studies. No-one reported problematic sleep. All were willing to participate in a 12-month study, answering one daily question using a phone app and wearing a wrist-device daily to capture activity, although night-time use was less acceptable. Recruitment via social media and doctors was perceived as optimal and compensatory monetary vouchers were favoured.

CONCLUSIONS: This PPI project identified patient-relevant endpoints of pain, stiffness and fatigue/ tiredness to be examined according to their interference of daily physical activities or socialising. Measurement using wearables and smartphones was viewed as acceptable and feasible for adolescents with XLH, which may therefore relieve burden on the healthcare system.