The purpose of this study is to better understand how X-linked hypophosphatemia (XLH) affects the body and daily life. Phosphate levels are critical in managing XLH, we aim to study how these levels change in patients taking burosumab and how they relate to bone health, overall disease burden and XLH-related conditions.

Inclusion Criteria:

• Informed consent obtained before any trial-related activities, i.e., any procedure related to recording of data according to the protocol.
• Male or female and aged 18-64 years (both inclusive) at the time of signing informed consent.
• Diagnosis of congenital XLH, confirmed genetically or clinically as determined by the investigator, supported by documentation.
• Participants have been treated with burosumab for at least 90 days prior to the screening/baseline visit and treatment is still ongoing.
• Participant confirms ability and willingness to attend visits according to routine clinical care and mandatory assessments at the site.

Exclusion Criteria:

• Previous rescreening for this trial.
• Current participation in any interventional clinical trial. Participation in another non-interventional trial, such as a patient registry trial, is permitted.
• Any condition not associated with XLH, which in the investigator's opinion might jeopardise participant's safety or compliance with the protocol.

Adults with XLH, confirmed genetically or clinically as determined by the investigator, who have been treated with burosumab for at least 90 days prior to the screening/baseline visit and whose treatment is still ongoing. Participants will be followed for a maximum of three years, continuing until end of trial visit, withdrawal of consent or loss to follow-up, whichever occurs first.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com