X-linked hypophosphatemia
hypophosphatemia (XLH) is an X-linked form of rickets that differs from most cases of dietary rickets in that vitamin D supplementation does not cure it. It can cause bone deformity, including short and genu varum (bow-leggedness). It is associated with a in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX . PHEX lead to an elevated circulating () level of the FGF23 which results in renal phosphate wasting, and local elevations of the mineralization/calcification-inhibiting protein osteopontin in the extracellular matrix of bones and teeth. An inactivating mutation in the PHEX gene results in an increase in systemic circulating FGF23, and a decrease in the enzymatic activity of the PHEX which normally removes (degrades) mineralization-inhibiting osteopontin protein. In XLH, the decreased PHEX enzyme activity leads to an accumulation of inhibitory osteopontin locally in bones and teeth to block mineralization, which, along with renal phosphate wasting, can cause osteomalacia and odontomalacia.
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Causes — why it happens
- ·A of the PHEX gene results in elevated FGF23 .
Complications
- ·osteomalacia (adults), rickets (children), fractures, enthesopathy, spinal , abnormal gait, short , tinnitus, hearing loss, dental , in rare exceptions Chiari can occur.