X-linked Hypophosphatemia (XLH)

X-linked hypophosphatemia (XLH) is a rare genetic disorder resulting from excess circulating fibroblast growth factor (FGF) 23, secondary to loss-of-function PHEX mutations (phosphate-regulating endopeptidase homolog, X-linked).

FGF23 is a protein hormone that regulates the appropriate phosphate levels in the body. Phosphate is a mineral that is essential for the normal formation of bones and teeth. Excess FGF23 causes the kidneys to waste phosphate into the urine, and reduces phosphate absorption in the intestines, resulting in chronically low blood levels of phosphate, which is also known as hypophosphatemia.

In children, chronic hypophosphatemia can result in a lifelong impact on skeletal health. It leads to bone disorders that result in abnormal bone formation, bone pain, lower-than-normal bone density, deformities in the legs, muscle pain and weakness.

The principal symptoms of XLH in adults are bone pain, joint pain, and stiffness. As patients age, long-term weight bearing on misaligned joints results in osteoarthritis.

XLH affects approximately 3,000 children and 9,000 adult patients in the U.S. It is typically diagnosed during childhood; however, some cases are not diagnosed until adulthood as the types and severity of symptoms can vary widely.

Other names for XLH:

  • Hypophosphatemic Rickets
  • X-Linked Hypophosphatemic Rickets
  • Familial Hypophosphatemia
  • Familial Hypophosphatemic Rickets
  • Vitamin D-Resistant Rickets
  • Genetic Rickets

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