X-linked Hypophosphatemia (XLH)
What is X-linked hypophosphatemia (XLH)?
X-linked hypophosphatemia (XLH) is an inherited disorder characterized by low levels of phosphate in the blood. These levels are low for those with XLH because phosphate is abnormally processed in the kidneys, which causes a loss of phosphate in the urine (phosphate wasting) and leads to soft, weak bones (rickets). XLH is usually diagnosed in childhood.
What are the symptoms of X-linked hypophosphatemia (XLH)?
XLH’s symptoms usually begin in early childhood and can vary in severity. They include:
- Noticeably bowed or bent legs
- Short stature
- Irregular skull growth
Overtime, symptoms may progress to include bone, joint, and/or dental pain. In rare instances, XLH may lead to hearing loss.
What causes X-linked hypophosphatemia (XLH)?
XLH is caused by mutations in the PHEX gene on the X chromosome. Mutations in this gene can lead to an increased concentration of fibroblast growth factor 23 (FGF23), a growth hormone that regulates the re-absorption of phosphate in the kidneys. Too much FGF23 causes phosphate wasting in the kidneys, preventing maintenance of proper phosphate levels in the blood, which causes the symptoms of XLH.
How is X-linked hypophosphatemia (XLH) diagnosed?
XLH is generally diagnosed after a physical exam, blood tests, imaging tests, genetic tests, and looking into family history. A slow growth rate and noticeable bowing of the legs, low levels of phosphate, high levels of FGF23 in the blood, and phosphate wasting in the kidneys are key factors to look for in diagnosing.
What are the available treatments for X-linked hypophosphatemia (XLH)?
Treatment aims at improving growth, bone or joint pain, and preventing skeletal deformities caused by rickets. Phosphate supplements are generally required and are typically combined with high dose calcitriol
, which increases calcium levels by increasing 1) the amount of calcium absorbed in the intestines and 2) the amount of calcium kept in the kidneys. Other treatment options include:
- Growth hormones to improve growth in children
- Corrective surgery to fix bowed or bent legs in children
- Treatment to repair skull abnormalities, such as premature fusion of the skull bones (synostosis)
Where can I find out more about X-linked hypophosphatemia (XLH)?