X-linked Hypophosphatemia (XLH)
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What Is X-linked Hypophosphatemia?
X-linked hypophosphatemia (XLH) is a rare inherited disorder that causes low levels of phosphorus (phosphate) in the blood. Our bodies need phosphate for muscles to move, nerves to work, and to build strong teeth and bones.
What Causes X-linked Hypophosphatemia?
XLH is caused by changes (mutations) in a gene called PHEX. These changes cause the body to make too much of a hormone called fibroblast growth factor 23 (FGF23). This hormone tells the body to get rid of more phosphate through urine, leading to low levels of phosphate in the blood.
This condition is usually passed down in families through the X chromosome. Males have one X chromosome (from their mother), and females have two X chromosomes (one from each parent). A child can inherit the condition from either parent, and only one copy of the changed gene is needed to develop XLH. Both males and females can have this condition.
What Are Signs & Symptoms of X-linked Hypophosphatemia?
Signs of XLH are often noticed when children start walking. They may have bowed legs or trouble walking. Other signs and symptoms include:
- Delayed walking
- Short height
- Gait abnormalities/Trouble walking
- Weak or painful muscles
- Bone or joint pain
- Dental problems, like infections or losing teeth
- An unusual head shape
- Feeling very tired
- Hearing loss
- Bone fractures
- Rickets
How Is X-linked Hypophosphatemia Diagnosed?
Your provider may do blood tests to check if phosphate levels are now, and check other labs, including calcium and kidney function tests. A genetic test can be done to evaluate for variants in the PHEX gene. Genetic testing can look for changes in the PHEX gene. X-rays, bone scans (DXA), or kidney ultrasounds may also help diagnose XLH.
How Is X-linked Hypophosphatemia Treated?
The goal of treatment is to increase phosphate levels. This may include phosphate supplements and a type of Vitamin D called calcitriol. Some patients may use a medicine called burosumab. This is an injection given every 2 to 4 weeks to lower FGF23 levels in the body.
Your care team may also include specialists from physical therapy, dentistry and/or nephrology.
What Are the Long-Term Effects of X-linked Hypophosphatemia?
Over time, XLH can cause fractures, hearing loss, and kidney problems.
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