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Parkes Weber syndrome
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Reviewed August 2011
What is Parkes Weber syndrome?
Parkes Weber syndrome is a disorder of the vascular system, which is the body's complex network of blood vessels. The vascular system consists of arteries, which carry oxygen-rich blood from the heart to the body's various organs and tissues; veins, which carry blood back to the heart; and capillaries, which are tiny blood vessels that connect arteries and veins.
Parkes Weber syndrome is characterized by vascular abnormalities known as capillary malformations and arteriovenous fistulas (AVFs), which are present from birth. The capillary malformations increase blood flow near the surface of the skin. They usually look like large, flat, pink stains on the skin, and because of their color are sometimes called "port-wine stains." In people with Parkes Weber syndrome, capillary malformations occur together with multiple micro-AVFs, which are tiny abnormal connections between arteries and veins that affect blood circulation. These AVFs can be associated with life-threatening complications including abnormal bleeding and heart failure.
Another characteristic feature of Parkes Weber syndrome is overgrowth of one limb, most commonly a leg. Abnormal growth occurs in bones and soft tissues, making one of the limbs longer and larger around than the corresponding one.
Some vascular abnormalities seen in Parkes Weber syndrome are similar to those that occur in a condition called capillary malformation-arteriovenous malformation syndrome (CM-AVM). CM-AVM and some cases of Parkes Weber syndrome have the same genetic cause.
Read more about capillary malformation-arteriovenous malformation syndrome.
How common is Parkes Weber syndrome?
Parkes Weber syndrome is a rare condition; its exact prevalence is unknown.
What genes are related to Parkes Weber syndrome?
Some cases of Parkes Weber syndrome result from mutations in the RASA1 gene. When the condition is caused by RASA1 gene mutations, affected individuals usually have multiple capillary malformations. People with Parkes Weber syndrome who do not have multiple capillary malformations are unlikely to have mutations in the RASA1 gene; in these cases, the cause of the condition is often unknown.
The RASA1 gene provides instructions for making a protein known as p120-RasGAP, which is involved in transmitting chemical signals from outside the cell to the nucleus. These signals help control several important cell functions, including the growth and division (proliferation) of cells, the process by which cells mature to carry out specific functions (differentiation), and cell movement. The role of the p120-RasGAP protein is not fully understood, although it appears to be essential for the normal development of the vascular system.
Mutations in the RASA1 gene lead to the production of a nonfunctional version of the p120-RasGAP protein. A loss of this protein's activity disrupts tightly regulated chemical signaling during development. However, it is unclear how these changes lead to the specific vascular abnormalities and limb overgrowth seen in people with Parkes Weber syndrome.
Read more about the RASA1 gene.
How do people inherit Parkes Weber syndrome?
Most cases of Parkes Weber syndrome occur in people with no history of the condition in their family. These cases are described as sporadic.
When Parkes Weber syndrome is caused by mutations in the RASA1 gene, it is sometimes inherited from an affected parent. In these cases, the condition has an autosomal dominant pattern of inheritance. Autosomal dominant inheritance means one copy of the altered gene in each cell is sufficient to cause the disorder.
Where can I find information about diagnosis or management of Parkes Weber syndrome?
These resources address the diagnosis or management of Parkes Weber syndrome and may include treatment providers.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about Parkes Weber syndrome?
You may find the following resources about Parkes Weber syndrome helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for Parkes Weber syndrome?
What if I still have specific questions about Parkes Weber syndrome?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding Parkes Weber syndrome?
arteries ; arteriovenous ; autosomal ; autosomal dominant ; capillaries ; cell ; cM ; congenital ; differentiation ; gene ; heart failure ; inheritance ; malformation ; nucleus ; oxygen ; pattern of inheritance ; prevalence ; proliferation ; protein ; RAS ; sporadic ; syndrome ; vascular ; veins
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (4 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.