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Parkes Weber syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Parkes Weber syndrome

Parkes Weber syndrome is a rare vascular disorder present from birth, characterized by capillary malformations, arteriovenous fistulas, and overgrowth of one limb, often caused by mutations in the RASA1 gene.

Overview

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.

Frequency

Parkes Weber syndrome is a rare condition; its exact prevalence is unknown.

Causes & Risk Factors

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 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.

Inheritance

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.

Other Names

  • Parkes-Weber syndrome
  • PKWS

Frequently Asked Questions

Key clues include a congenital port‑wine stain (capillary malformation) over the enlarged limb, the presence of palpable warm pulsations or a thrill from underlying arteriovenous fistulas, and radiographic evidence of both soft‑tissue and bony overgrowth. Genetic testing that identifies a pathogenic RASA1 variant also supports Parkes Weber, whereas other conditions have distinct skin findings or lack AV fistulas.
Signs of high‑output cardiac failure include rapid breathing, persistent fatigue, swelling of the ankles or abdomen, and a newly audible heart murmur. If the child develops unexplained tachycardia, shortness of breath at rest, or a drop in blood pressure, immediate cardiology assessment with echocardiography is warranted, as untreated AV shunting can lead to heart failure.
Management is multidisciplinary. Endovascular embolization or surgical ligation of dominant AV fistulas can reduce blood flow and slow overgrowth. Orthopedic procedures (epiphysiodesis, limb‑lengthening, or epiphyseal arrest) address bone length discrepancy. Laser therapy or pulsed‑dye laser can lighten the capillary stain for cosmetic reasons. Physical therapy helps maintain range of motion and strength.
Testing usually involves a blood sample sent for targeted sequencing or a multigene panel that includes RASA1. A pathogenic variant confirms the diagnosis and indicates an autosomal‑dominant inheritance pattern, meaning each first‑degree relative has a 50 % chance of carrying the mutation. Genetic counseling can discuss prenatal testing, pre‑implantation genetic diagnosis, and surveillance recommendations for at‑risk family members.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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