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A congenital vascular bone syndrome with the presence of a vascular malformation in a limb, mainly of the arteriovenous type, which results in overgrowth of the affected limb. The affected limb may show overgrowth in comparison with the contralateral limb and the extent of this limb length discrepancy may vary from a slight difference to 10cm or more. The growth effect may be manifested in only one bone (mainly the femur or tibia) or, in some cases, affect the whole limb. The existence of arteriovenous fistulas around or inside the bone is now being widely accepted as the main cause of bone overgrowth. Although the syndrome generally appears to be sporadic, autosomal dominant inheritance has been noted in a few families.
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A syndrome affecting the development of blood vessels, soft tissue and bone with three characteristic features: port-wine stain, abnormal overgrowth of soft tissues and bones and venous malformations. Caused by mutations in the PIK3CA gene. This gene provides instructions for making the p110 alpha (p110α) protein, which is a subunit of phosphatidylinositol 3-kinase (PI3K). The PIK3CA gene mutations associated with Klippel-Trenaunay syndrome alter the p110α protein. The altered subunit makes PI3K abnormally active, which allows cells to grow and divide continuously. Increased cell proliferation leads to abnormal growth of the bones, soft tissues, and blood vessels. This syndrome is almost always sporadic meaning it can occur in people with no history of the disorder in their family. Studies suggest that the condition results from gene mutations that are not inherited.
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