X-linked hypophosphatemia (XLH) is a rare genetic disease characterized by low phosphate levels in the blood, which leads to a number of symptoms in children and adults. These symptoms vary widely in their severity between patients.

Bone abnormalities

Children with XLH generally show delayed growth and short stature, with deformed leg bones such as knock knees and bowed legs. Their bones are also softer than normal (rickets and osteomalacia), which can cause bone and joint pain. Unlike other rickets, rickets caused by XLH does not respond to vitamin D treatment.

During development, the plates in the skull of children with XLH can merge irregularly and cause craniosynostosis. For some patients, the base of the brain can extend into the opening of the bottom of the skull in a condition called Chiari malformation, which can cause severe headaches.

These childhood symptoms can be exacerbated in adults with XLH, whose weak and soft bones make fractures more likely. Osteoarthritis can also develop in adult patients and cause inflammation in joints. Some tendons and ligaments may calcify, i.e. abnormal calcium deposits form on them, causing pain in the joints and impeding movement.

Many adult patients with XLH also experience hearing loss.

Muscle weakness and pain

Muscles need healthy bones to function normally. Weakened and malformed bones due to XLH mean that children with the disease may also have weak or stiff muscles that can cause pain, especially during movement. Many children with the disease have a distinctive “waddling” gait.

These muscle symptoms usually persist into adulthood and may become more severe as the patient ages.

Teeth problems

Children with XLH are prone to tooth abscesses or infections under the teeth. Their teeth may also be spaced irregularly, which leads to pain and infections that may necessitate the removal of teeth.

Adults with XLH are also prone to tooth abscesses and may even develop periodontitis, a serious gum disease.


Last updated: Dec. 5, 2019


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