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Diagnosis of XLH usually happens in childhood, but can happen in infancy and adulthood too. Here’s what to expect.

XLH is a lifelong condition with symptoms that vary between children and adults, and from person to person. XLH is caused by an alteration (mutation) in a gene called PHEX which is located on the X-chromosome (hence the name ‘X-linked hypophosphatemia’).

Most people (two out of three) with XLH inherit the PHEX mutation from a parent. Knowing that XLH is present in a family often helps to quicken the diagnosis of newborns with the condition.

Around one in three people with XLH spontaneously develop the PHEX mutation.  This is called spontaneous XLH because there is no family history of XLH.

Childhood diagnosis

XLH symptoms first tend to appear between the ages of 6 and 18 months – the time at which most of us first learn to walk. Common symptoms are:

  • Bowed legs or knock-knees
  • Big wrists and/or knees
  • Delayed growth (short stature)
  • A waddling gait
  • Teeth abscesses (once teeth develop) 
  • Bone, muscle or joint pain 
  • Unusual head shape 

Because XLH is a rare condition, it can sometimes be misdiagnosed as:

  • Nutritional rickets (due to low amounts of vitamin D in the diet)
  • Pyle’s disease (a condition where the outsides of long bones are thinner than they should be)
  • Leg bowing related to normal growth
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Early diagnosis helps

Studies suggest that the sooner XLH is correctly diagnosed and treatment is started, the better. So it’s important that any newborn child related to anyone with XLH is tested for the condition as soon as possible. The tests may involve:

  • Taking blood samples
  • Taking urine samples
  • X-rays
  • Genetic testing

As a parent, it can be hard watching your child go through these tests and then wait for the results. Having a child diagnosed with XLH can be very upsetting, even if there’s a history of XLH in your family. It’s likely to have a big emotional impact. Remember to talk to your child’s healthcare team about any concerns. They will be able to advise and support you as your child goes through the diagnosis process.

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Keeping a health diary

It’s not easy remembering everything healthcare professionals tell you. So it’s a good idea to keep a diary to record symptoms, appointment dates, notes about medicines and any questions you may have. The more engaged you are, the easier the diagnosis process will be for you and your children.

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Diagnosis in adulthood

XLH is usually diagnosed during childhood but it can be missed or misdiagnosed, particularly if a child’s symptoms are mild or if there’s no family history of XLH. Consequently, some people reach adulthood with symptoms such as:

  • Pseudofractures 
  • Osteoarthritis
  • Joint pain and stiffness
  • Enthesopathy (ligament problems) 
  • Bone pain
  • Dental abscesses 
  • Hearing problems
  • Fatigue
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Coping with a lifelong condition

A mistake that people with XLH sometimes make is that they assume XLH is a childhood disease. As adolescents grow to become adults, their symptoms change and can become less severe, which can make them think their XLH has passed. Understandably, many people stop taking their medicines or stop seeing their healthcare team. But sadly, XLH doesn’t go away – it’s a lifelong condition and many people need to have their symptoms managed throughout their adult lives.

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Your feelings are important too

Learning that your XLH has ‘come back’ or being diagnosed for the first time as an adult can be an upsetting experience. So, make sure you get enough support from your family and your healthcare team. Having someone to talk to can make a big difference. 

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XLH Link - HCP Website

This Kyowa Kirin website is intended for Healthcare Professionals (HCPs) involved in the care of people with X-linked Hypophosphatemia (XLH).

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