Endocrine Abstracts

Background: X-linked hypophosphataemia (XLH) is a genetic condition that causes significant skeletal deformities and is associated with lifelong disability and pain. In October 2018, the NHS in England recommended burosumab, an anti-FGF23 antibody, for treating XLH with radiographic evidence of bone disease in children aged 1 year and over, and in young people with growing bones. The clinical and cost effectiveness of burosumab for treating adults with XLH is being assessed.

Purpose: There is a lack of data reporting outcomes in patients who have experienced cessation of burosumab therapy at the end of bone growth. This multi-centre case series shares real-world experience of burosumab cessation in such patients.

Methods: Descriptive report of four patients with XLH from three centres in England. Medical history and biochemical and radiological findings, as well as patient and caregiver experiences, are reported.

Results: Two female patients were diagnosed prior to symptoms, having had a family member with a confirmed PHEX mutation, two (one female, one male) were diagnosed in early childhood (2 and 5 years old, respectively) after presenting with symptoms. All patients initially received conventional therapy (oral phosphate and active vitamin D). Symptoms during this time included skeletal deformity, pain, stiffness, gait disturbance, limited mobility and psychological effects. All patients were switched to burosumab and were treated for 2–4 years until the end of growth. During this time, one patient was reported as demonstrating leg straightening. Patients had improvements in bone biochemistry markers. Patients reported quicker recovery from orthopaedic surgery than when they were on conventional therapy, reduction in pain and stiffness, improved mobility, higher energy and activity levels, and improved school attendance. Following cessation of burosumab at the end of bone growth, patients subsequently reported experiencing more pain, less energy, reduced mobility and consequences on work and psychological wellbeing. Two of the patients had been changed back to conventional therapy.

Conclusion: These cases provide some insights into patient course after cessation of burosumab at the end of bone growth. Stopping treatment led to symptom recurrence and reduced patient wellbeing, suggesting that re-initiation of treatment may be warranted.