Frequently Asked Questions QUESTION: What is XLH? ANSWER:
X-chromosome Linked Hypophosphatemia is a genetic metabolic
disorder that usually results in bowed or bent legs in growing
children. In XLH, the body's mechanisms to make and maintain
bones and teeth do not work correctly. One of the things needed
for good bone growth is the mineral phosphorus. The key
characteristic of XLH -- low phosphorus in the blood, also known
as hypophosphatemia -- is the result of a mutation that
essentially inactivates one of the genes on the X chromosome.
When this gene, called the PHEX gene, has the XLH mutation, a
protein circulating in the bloodstream called FGF23 increases,
causing the kidneys to waste phosphorus and suppresses complete
activation of vitamin D to a form the body can use. The loss of
phosphate from the kidneys prevents the body from maintaining
the proper level of phosphorus in the blood. Q: Is there a
single mutation responsible for XLH? A: So far, approximately
260 different mutations in a particular sec