Klippel-Trenaunay (klih-PEL tray-no-NAY) syndrome ― also called KTS ― is a rare disorder found at birth (congenital) involving problems in the development of certain blood vessels, soft tissues (such as skin and muscles), bones and sometimes the lymphatic system. The main features include a red birthmark (port-wine stain), ranging in color from pink to reddish-purple, atypical vein or lymphatic development (malformations), and overgrowth of tissues and bones. These findings most often affect one leg but may occur in an arm or elsewhere.

Although there is no cure for KTS, treatment goals are to improve symptoms and prevent complications.


People who have KTS may have the following features, which can range from mild to more extensive:

  • Port-wine stain. This pink to reddish-purple birthmark is caused by extra tiny blood vessels (capillaries) in the top layer of skin. The birthmark often covers part of one leg but can involve any portion of the skin. It may get darker or lighter with age.
  • Vein malformations. These include swollen, twisted veins (varicose veins), usually on the surface of the legs. Deeper malformed veins in the arms, legs, abdomen and pelvis also can occur. There may be spongy tissue filled with small veins in or under the skin. Malformed veins may become more prominent with age.
  • Overgrowth of bones and soft tissue. This begins in infancy and may be limited to one leg, but it can occur in an arm or, rarely, in the trunk or face. This overgrowth of bone and tissue creates a larger and longer extremity. Rarely, there may be fusion of fingers or toes or extra fingers or toes.
  • Lymphatic system malformations. The lymphatic system — part of the immune system that protects against infection and disease and transports lymphatic fluid — can be malformed. Extra lymphatic vessels can be present that don't work properly and can lead to fluid leakage into the tissues and swelling.
  • Other conditions. KTS can also include cataracts, glaucoma, hip dislocation at birth, purple-red skin coloring when cold and blood-clotting problems.

When to see a doctor

KTS is usually identified at birth. It's important to get a prompt, accurate diagnosis and appropriate care to treat symptoms and prevent complications.


KTS is a genetic disorder. It involves genetic changes (mutations), most commonly in the PIK3CA gene. This gene is responsible for the growth of cells and the development of tissues in the body. A change in this gene results in overgrowth of tissues.

KTS is not usually inherited. The gene changes occur randomly during cell division in early development before birth.

Risk factors

Family history doesn't seem to be a risk factor, so it's unlikely that parents of one child with KTS will have another child with the disorder, even if one of the parents has KTS.


Complications of KTS can result from atypical development of blood vessels, soft tissues, bones and the lymphatic system. These can include:

  • Port-wine stain complications. Some areas of the port-wine stain may thicken over time and may form blisters (blebs) that are prone to bleeding and infections. Skin ulcers and poor wound healing also may occur.
  • Vein malformations. Varicose veins can cause pain and skin ulcers due to poor circulation. Deeper malformed veins can increase the risk of blood clots (deep vein thrombosis) and cause a life-threatening condition called pulmonary embolism if the clots dislodge and travel to the lungs. Venous malformations in the pelvis and abdominal organs can cause internal bleeding. Superficial veins can develop less serious but painful clots and inflammation (superficial thrombophlebitis).
  • Overgrowth of bones and soft tissue. Overgrowth of bone and tissue can cause pain, a feeling of heaviness, limb enlargement and problems with movement. Overgrowth that causes one leg to be longer than the other can result in problems with walking and may lead to hip and back problems.
  • Lymphatic system malformations. Malformations in the lymphatic system can cause fluid buildup and swelling in the tissues of the arms or legs (lymphedema), skin breakdown and skin ulcers, leakage of lymphatic fluid, or infection of the layer under the skin (cellulitis).
  • Chronic pain. Pain can be a common problem that results from complications such as infections, swelling, bone involvement or vein problems.