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Diagnosis of XLH
By: Larry Winger, Ph.D., PGCE & Scott Schmitz XLH is a genetic disorder of bone metabolism. It is expressed in varying degrees in terms of bone involvement, but it is always manifest in affected individuals by abnormally low serum inorganic phosphorus levels, as first documented by Winters et al in 1958, based on extensive family studies in the Carolinas. Because XLH can also be sporadic (i.e. spontaneous cases arrive de novo with no previous family history), it's important to differentiate between diagnosis when there is a family history and diagnosis when there is no family history. In principle, diagnosis of an individual infant or toddler when there is a family history of XLH should be straightforward, but the direct and compelling experience of too many in the XLH Network has been that this diagnosis has often been misconstrued, even by experts in the field. In too many cases, it appears that there is a discrepancy between what are interpreted as normal values for serum inorganic phosphorus, and what age-matched normal values really are. We provide here examples with citations of normal values for serum inorganic phosphorus relative to the age of the normal subjects. We urge pediatricians considering the evidence from their clinical chemistry laboratories, when attempting to diagnose children where there is a known family history of XLH, carefully to compare the results of their subject 's serum inorganic phosphorus levels with these known values for young children. In particular, it may be instructive for the clinical chemistry laboratory used by the pediatrician to report their direct experience of phosphorus levels in age-matched normals. The consensus among medical professionals is that the earlier treatment for XLH can start, the better the prognosis in terms of good bone growth and development, and obviously the less opportunity for deformities of the lower limbs to progress beyond control When there is a family History of XLH When there is NO family history of XLH The mailing list for The XLH Network Inc. is privileged to count among its membership some of the world's best clinicians and researchers in the XLH field, and the coordinators are delighted to pass along professional enquiries and correspondence to these members, if further consultation would be beneficial. Please feel free to contact us with your enquiries. A parents and patients perspective of diagnosis is available here.
References
X-linked hypophosphatemic rickets: a disease often unknown
to affected patients. Diagnosis of X-linked hypophosphatemic vitamin D resistant rickets.
Hypophosphatemic rickets: still misdiagnosed and inadequately
treated. 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 spotaneous dental abscesses, and low blood phosphorus levels.
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