About X-Linked Hypophosphatemia
X-linked hypophosphatemia is the most common hereditary form of rickets, caused by loss-of-function variants in PHEX, a phosphate-regulating endopeptidase that normally suppresses FGF23 production; PHEX deficiency leads to inappropriately elevated circulating FGF23, renal phosphate wasting, and impaired vitamin D activation. The resulting hypophosphataemia causes defective skeletal mineralisation, bowed legs, growth retardation, dental abscesses from abnormal dentine, and musculoskeletal pain throughout life. Burosumab, an anti-FGF23 monoclonal antibody, represents targeted therapy and has transformed the treatment landscape.
Common Clinical Features
Clinical Trial Eligibility Tips
What to know before applying to X-Linked Hypophosphatemia trials.
Serum phosphorus, TRP (tubular reabsorption of phosphate), and FGF23 levels are key biomarkers at screening — ensure these are drawn fasting and that current conventional therapy (phosphate and calcitriol) is documented.
Prior or current burosumab treatment is a frequent exclusion criterion in investigational trials; confirm last dose date and current treatment regimen with the trial coordinator.
Wrist and knee radiographs graded for rachitic severity (Thacher score or equivalent) are standard baseline requirements in paediatric trials.
Patient Resources
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