Health condition
X-linked hypophosphataemia
X-linked hypophosphataemia (XLH) is an inherited phosphate-wasting disorder causing bowed legs, short stature, dental abscesses and adult bone and joint pain - now treatable with burosumab, which targets the underlying mechanism.
Why trust this guide
- 01
Editorial team
Written by our editorial team from the UK sources listed on each page.
- 02
Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
- 03
Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
Which gene and test confirm it, who should be tested in the family, and which specialist to see.
-
Caused by PHEX gene variants; X-linked dominant - affected fathers pass it to all daughters and no sons; affected mothers pass it to half their children
-
The kidney wastes phosphate under the influence of excess FGF23; blood phosphate is low, but the condition is often missed because phosphate is not routinely checked
-
Adult features: enthesopathy (stiff, calcified tendon insertions), osteomalacia, pseudofractures, dental abscesses, hearing problems
-
Burosumab, an anti-FGF23 antibody, has transformed treatment for children and is available for symptomatic adults
Understanding the condition
What it is and what happens next.
What causes it, how it is confirmed, and the testing and specialist routes available in the UK.
What it is and how it presents
XLH used to be filed under childhood rickets, corrected legs and case closed - but the phosphate leak never stops, and adults accumulate their own burden: aching, stiffening tendon insertions, poorly healing stress fractures in the femur or feet, spontaneous dental abscesses in apparently healthy teeth, and joint degeneration from decades of altered mechanics. Many adults with milder disease were never diagnosed at all, carrying 'bandy legs' and chronic pain without a name.
Testing, surveillance and specialist care
The laboratory picture - low phosphate with inappropriate urinary phosphate loss and a raised or unsuppressed FGF23 - points to the diagnosis, and PHEX sequencing confirms it while clarifying the X-linked inheritance for family testing. Specialist metabolic bone clinics assess adults for conventional therapy or burosumab and coordinate dental, orthopaedic and audiology care. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged 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 endocrinologist at a metabolic bone service. 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 emergency symptoms.
Frequently asked
Common questions about X-linked hypophosphataemia.
Quick, plain-English answers to what people ask us most.
-
What is X-linked hypophosphataemia?
It is a rare inherited condition in which the kidneys excrete too much phosphate, leading to weakened, poorly mineralised bones.
-
What causes X-linked hypophosphataemia?
It results from mutations in the PHEX gene, leading to excess of a hormone called FGF23, which causes the kidneys to lose phosphate; it's inherited in an X-linked dominant pattern.
-
What are the symptoms of X-linked hypophosphataemia?
In children, bowed legs, short stature, and delayed growth are typical; in adults, bone and joint pain, muscle weakness, and dental problems are common.
-
Is X-linked hypophosphataemia dangerous?
It isn't life-threatening, but untreated bone weakness can lead to significant deformity, pain and reduced mobility over time.
-
Is X-linked hypophosphataemia hereditary?
Yes, it's inherited in an X-linked dominant pattern, affecting both males and females, with an affected parent having a 50% chance of passing it to each child.
-
Can X-linked hypophosphataemia be treated?
Yes, treatment with phosphate and active vitamin D supplements, or a newer targeted medication (burosumab), can significantly improve bone health and symptoms.
-
How is X-linked hypophosphataemia treated?
Traditional treatment involves phosphate and calcitriol supplementation; burosumab offers a more targeted approach by directly addressing the underlying hormone imbalance driving phosphate loss.
-
How is X-linked hypophosphataemia diagnosed?
Diagnosis involves blood tests showing low phosphate with high FGF23 levels, characteristic changes on X-ray, and often genetic testing to confirm the PHEX gene mutation.
-
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.