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 usually diagnosed in childhood. Features include bowed or bent legs, short stature, bone pain, and severe dental pain. XLH is caused by mutations in the PHEX gene on the X chromosome, and inheritance is X-linked dominant. Treatment 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.