What is XLH? X-linked hypophosphatemia (XLH) is an inherited disorder characterised by low levels of phosphate in the blood. Phosphate levels are low 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.
XLH is caused by mutations in the PHEX gene on the X chromosome, and inheritance is X-linked dominant. The key characteristic of XLH–low phosphorus in the blood—is the result of a mutation that inactivates one of the genes on the X Chromosome (hence the “X” in XLH). That means XLH is transferred genetically. However, XLH can appear in an individual with no known family history.
Patients with XLH experience abnormal bone and tooth development. Many develop rickets, presenting with knock-knees or bowing of the legs. Other symptoms include:
- unusual gait
- short stature or declining growth rate
- spontaneous tooth abscesses
- bone pain, muscle pain and weakness.
Diagnosis of XLH is usually made during childhood, with the symptoms of XLH often apparent before a child begins to walk. XLH is often undiagnosed or misdiagnosed as simple Vitamin D deficiency because it is a rare genetic condition. In the average person, normal diets and sunlight exposure successfully treat Vitamin D deficiency and conditions like rickets, but for people with XLH, this does not work. Early diagnosis is extremely important for effective XLH treatment. XLH Australia Inc is committed to empowering XLH-affected individuals and their families to successfully advocate for their diagnosis.
XLH is not curable, but it is treatable. Treatment for XLH generally involves supplements of phosphate and high-dose calcitriol (the active form of Vitamin D), and may also include growth hormones, corrective surgery, and dental treatment.
The long-term outlook varies depending on severity and whether complications arise. While some adults with XLH may have minimal medical problems, others may experience persistant discomfort or complications.