By: The XLH Network Inc. Coordinators

These are the names for a relatively rare metabolic disorder that affects about 1 in 20,000 people. The name typically used by professionals today is X-Linked Hypophosphatemia which is generally referred to by its acronym: XLH. Another very rare genetic disorder recently described with similar symptoms is Autosomal Dominant Hypophosphatemic Rickets (ADHR) .

XLH is a genetic disorder that is passed from one generation to the next. Like other genetic disorders it can also sometimes appear in an individual with no family history of XLH, in which case it is called a spontaneous or sporadic occurrence. XLH is carried on the X chromosome; hence the 'X-Linked' in the name. The rest of the name, hypophosphatemia, identifies the primary and key sign of XLH, which is a low level of phosphorus in the blood. Knock-knees or bowing of the legs are the most noticeable symptoms of the rickets disorder which can occur as a result of hypophosphatemia, although these symptoms may be mild, moderate or severe in different individuals with XLH. In adults, the bone disease is called osteomalacia, that is, soft bones.

Vitamin D-Resistant Rickets was the term first used for this disorder since XLH was initially recognized by the ineffectiveness of normal diets to prevent rickets from developing. Any children that do not get enough sunlight exposure, or receive insufficient Vitamin D in their diet, are at risk of developing rickets because bones need Vitamin D for proper growth and development. Normal diets usually contain sufficient Vitamin D in milk, meat or fish, but people with XLH are 'resistant' to this Vitamin D, though they can respond to other more active forms of this vitamin hormone. Today the syndrome is defined more by the root cause of the disorder, based on phosphorus metabolism, rather than on the role played by Vitamin D.

The XLH Network Inc. also seeks to provide support for people with similar bone disorders which may arise because of problems with a different component in the shared control system that regulates phosphorus levels. People with the recently described Autosomal Dominant Hypophosphatemic Rickets disorder can have symptoms that differ only in subtle ways from those experienced by people with XLH.

Very rare bone tumours or rare cases of giant nevus sebaceous may also cause bone problems due to hypophosphatemia. We are learning that we can learn from each other.

Last modified Aug 8, 2007

XLH is also known as X-Linked Hypophosphatemia (sometimes also spelled as hypophosphataemia), X-Linked Hypophosphatemic Rickets, Familial Hypophosphatemia, Vitamin D-Resistant Rickets (VDRR) Rickets and even Genetic Rickets. Its notable characteristics are bowed legs, short stature, poor teeth formation causing spontaneous dental abscesses, and low blood phosphorus levels.

© 2002-2007, The XLH Network Inc.
The authors of this web site are not medical professionals, and this information does not substitute for medical care. Information on these pages is based on biomedical research, published in peer-reviewed journals, and international research conferences. Additionally, in some cases anecdotal information is provided by subscribers of the F-HYPDRR group, a mailing list for The XLH Network Inc. A complete web-site bibliography is available. Please read our full disclaimer.