Klippel-Trenaunay syndrome

Klippel-Trenaunay syndrome is a condition that affects the development of blood vessels, soft tissues, and bones. The disorder has three characteristic features: a red birthmark called a port-wine stain, abnormal overgrowth of soft tissues and bones, and vein malformations.

Most people with Klippel-Trenaunay syndrome are born with a port-wine stain. This type of birthmark is caused by swelling of small blood vessels near the surface of the skin. Port-wine stains are typically flat and can vary from pale pink to deep maroon in color. In people with Klippel-Trenaunay syndrome, the port-wine stain usually covers part of one limb. The affected area may become lighter or darker with age. Occasionally, port-wine stains develop small red blisters that break open and bleed easily.

Klippel-Trenaunay syndrome is also associated with overgrowth of bones and soft tissues beginning in infancy. Usually this abnormal growth is limited to one limb, most often 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. If the overgrowth causes one leg to be longer than the other, it can also lead to problems with walking.

Malformations of veins are the third major feature of Klippel-Trenaunay syndrome. These abnormalities include varicose veins, which are swollen and twisted veins near the surface of the skin that often cause pain. Varicose veins usually occur on the sides of the upper legs and calves. Veins deep in the limbs can also be abnormal in people with Klippel-Trenaunay syndrome. Malformations of deep veins increase the risk of a type of clot called a deep vein thrombosis (DVT). If a DVT travels through the bloodstream and lodges in the lungs, it can cause a life-threatening clot known as a pulmonary embolism (PE).

Complications of Klippel-Trenaunay syndrome can include a type of skin infection called cellulitis, swelling caused by a buildup of fluid (lymphedema), and internal bleeding from abnormal blood vessels. Less commonly, this condition is also associated with fusion of certain fingers or toes (syndactyly) or the presence of extra digits (polydactyly).

Klippel-Trenaunay syndrome is estimated to affect at least 1 in 100,000 people worldwide.

The cause of Klippel-Trenaunay syndrome is unknown. Researchers suspect that the condition may result from changes in one or more genes that regulate the growth of blood vessels during embryonic development. However, no associated genes have been identified. It is also unclear how blood vessel malformations are related to the overgrowth of bones and soft tissues.

Klippel-Trenaunay syndrome is almost always sporadic, which means that it occurs in people with no history of the disorder in their family. Studies suggest that the condition may result from gene mutations that are not inherited. These genetic changes, which are called somatic mutations, probably occur very early in development and are present only in certain cells. Somatic mutations could explain why the signs and symptoms of Klippel-Trenaunay syndrome are often limited to specific areas of the body. However, it is unclear whether somatic mutations are responsible for this condition because no associated genes have been found.

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