A parent taking a picture of their toddler


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
Read more Read less

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.

Read more Read less

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.

Read more Read less

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
Read more Read less

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.

Read more Read less

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. 

Read more Read less

Welcome to
XLH Link

This website is specifically designed to provide information about X-Linked Hypophosphatemia (XLH) and assist with the correct assessment of the condition.
Please note that this website does not replace the role of a Healthcare Professional and it is always recommended that you seek professional medical advise if symptoms persist.

To continue to the website please select your country



United Kingdom

If your country is not listed please go to the European page below

XLH Link

You are about to leave a Kyowa Kirin website

You are leaving the XLH Link website to a site that is not under the control of Kyowa Kirin. Kyowa Kirin is not responsible for the content of any such site or any further link from such site. Are you sure you want to continue?

Yes No

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).

Please confirm you are a healthcare professional

Yes, I am a healthcare professional No, I am not a healthcare professional
We use cookies to ensure that we give you the best website experience. By continuing to use this site, you are agreeing to our use of cookies.