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 Mar 27, 2011
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.
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
is available. Please read our full