X-linked hypophosphatemia (XLH) is an inherited disorder characterized 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 (rickets). XLH is usually diagnosed in childhood. Features include bowed or bent legs, short stature, bone pain, and severe dental pain. XLH is caused by genetic changes in the PHEX gene on the X chromosome, and inheritance is X-linked dominant.