Health condition
X-linked hypophosphataemia: a deep dive
X-linked hypophosphataemia (XLH) is a genetic disorder in which the hormone FGF23 makes the kidneys waste phosphate, softening bones lifelong; adults have osteomalacia, enthesopathy and early arthritis, and the antibody treatment burosumab has changed management.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
The symptoms to recognise, when to seek help, which specialist to see, and what treatment usually involves.
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Caused by PHEX mutations that raise FGF23, driving renal phosphate wasting - serum phosphate is persistently low
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Adult burden: bone and joint pain, pseudofractures, stiffness from calcifying entheses, early osteoarthritis, dental abscesses and hearing problems
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Diagnosis: low phosphate with inappropriate urinary phosphate loss (low TmP/GFR), raised FGF23 and genetic confirmation
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Burosumab, an anti-FGF23 antibody, is available for XLH and treats the cause; conventional therapy (phosphate salts plus active vitamin D) remains an option
Understanding the condition
What it is and what happens next.
What causes it, how it is diagnosed, and the treatment routes available in the UK.
What it is and how it feels
XLH is usually diagnosed in childhood through bowed legs and growth problems, but the adult phase is quietly disabling in its own way: chronic osteomalacia makes bones ache and crack, tendon and ligament insertions calcify into stiffness, spinal ligament ossification can narrow the canal, and teeth abscess without cavities. Adults who "grew out of rickets clinics" often drift from specialist care exactly when symptoms accumulate.
Diagnosis and treatment routes
Re-establishing care in a metabolic bone service allows proper assessment - phosphate handling studies, FGF23 measurement, imaging of pseudofractures and entheses - and a treatment decision between burosumab (NICE-approved in the UK for XLH, given by injection every four weeks in adults with significant disease) and conventional phosphate/calcitriol regimens with their monitoring burdens. Dental surveillance, hearing checks and genetic counselling for children (daughters of affected men will all inherit the variant) complete the picture. In much of the UK, a routine NHS referral to the relevant specialist clinic can take several months, whereas an initial appointment with a private consultant is typically available within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a metabolic bone specialist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any of the emergency symptoms described above.
Frequently asked
Common questions about X-linked hypophosphataemia: a deep dive.
Quick, plain-English answers to what people ask us most.
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What is X-linked hypophosphataemia?
It is a rare inherited condition causing the kidneys to lose excessive amounts of phosphate, leading to weak, poorly mineralised bones (rickets in children, osteomalacia in adults).
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What causes X-linked hypophosphataemia?
It is caused by mutations in the PHEX gene, leading to excess levels of a hormone (FGF23) that causes the kidneys to waste phosphate; it's inherited in an X-linked dominant pattern, affecting both males and females, though often more severely in males.
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What are the symptoms of X-linked hypophosphataemia?
In children, this includes bowed legs, short stature, and delayed walking; in adults, symptoms often include bone and joint pain, muscle weakness, dental problems, and sometimes early-onset osteoarthritis-like symptoms.
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Is X-linked hypophosphataemia dangerous?
It isn't immediately life-threatening, but untreated bone weakness can cause significant deformity, pain, and mobility problems over a lifetime, so ongoing specialist management is important.
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Is X-linked hypophosphataemia hereditary?
Yes, it's inherited in an X-linked dominant pattern, meaning an affected parent has a 50% chance of passing the condition to each child, affecting both sons and daughters, though sons who inherit it are often more severely affected.
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Can X-linked hypophosphataemia be treated?
Yes, traditional treatment with phosphate and active vitamin D supplements can help manage symptoms, and a newer targeted medication (burosumab) that directly addresses the underlying FGF23 hormone excess has significantly improved treatment options.
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How is X-linked hypophosphataemia treated?
Treatment includes phosphate and calcitriol (active vitamin D) supplementation, or the newer targeted therapy burosumab, which works upstream to correct the underlying phosphate-wasting mechanism more directly.
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How is X-linked hypophosphataemia managed long-term?
Ongoing management involves regular monitoring of bone health, growth (in children), kidney function, and specific treatment adjustments, ideally coordinated by a specialist in metabolic bone disease familiar with this condition.
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When should I see a specialist, and how quickly can I be seen privately?
See an endocrinologist specialising in metabolic bone disease. NHS specialist clinics can have long waits; private specialists can often see you within about two weeks.