Klippel Trenaunay syndrome
is a condition that affects the development of blood vessels, soft tissues, and bones. This condition has three characteristic features: a red birthmark called a port-wine stain, abnormal overgrowth of soft tissues and bones, and vein malformations. A port-wine stain is a type of birthmark caused by swelling of the small blood vessels near the surface of the skin. The overgrowth of bones and soft tissues usually begins in infancy and is most often limited to one leg. However, overgrowth can also affect the arms or, rarely, the trunk. The abnormal growth can cause pain, a feeling of heaviness, and reduced movement in the affected area. The vein malformations include varicose veins and malformations of deep veins in the limbs. The cause of Klippel-Trenaunay syndrome is unknown. This condition is almost always sporadic, which means that it occurs in people with no history of the disorder in their family. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.