What Is Osler-Weber-Rendu Syndrome?

Osler-Weber-Rendu syndrome (OWR) is also known as hereditary hemorrhagic telangiectasia (HHT). It’s a genetic blood vessel disorder that often leads to excessive bleeding. According to the HHT Foundation International, the syndrome affects about one in 5,000 people. However, many people with the disease don’t know they have it, so this number may actually be higher.

The name Osler-Weber-Rendu syndrome is named for the doctors who worked on researching this condition in the 1890s. They discovered that issues with blood clotting don’t cause this condition, which was previously assumed. Instead, this condition is caused by problems with the blood vessels themselves.

In a healthy circulatory system, there are three types of blood vessels. There are arteries, capillaries, and veins. Blood moving away from your heart is carried through arteries, which travels at a high pressure. Blood moving towards your heart is carried through veins, and it travels at a lower pressure. The capillaries sit between these two types of blood vessels, and the narrow passageway of your capillaries helps to lower the pressure of the blood before it reaches the veins.

People with OWR are missing capillaries in some of their blood vessels. These abnormal blood vessels are known as arteriovenous malformations (AVM).

Because there’s nothing to lower the pressure of the blood before it flows into the veins, people with OWR often experience strained veins that may eventually rupture. When large AVMs occur, hemorrhages can occur. Hemorrhages in these areas can become life-threatening:

  • the brain
  • the lungs
  • the liver
  • the gastrointestinal tract

People with OWR also have abnormal blood vessels called “telangiectasias” near the skin and mucosal surfaces. These blood vessels are dilated, or widened, and are often visible as small red dots on the skin surface.

Symptoms and signs of OWR and their severity vary widely, even among family members.

A common sign of OWR is a large red birthmark, sometimes called a port wine stain. A port-wine stain is caused by a collection of dilated blood vessels, and it may darken in color as the person ages.

Telangiectasias are another common symptom of OWR. They’re often small red dots and are prone to bleeding. The marks may appear on young children or not until after puberty. Telangiectasias can appear on the:

  • face
  • lips
  • tongue
  • ears
  • fingertips
  • whites of the eyes
  • gastrointestinal system

AVMs can occur anywhere inside the body. The most common sites are:

  • the nose
  • the lungs
  • the gastrointestinal tract
  • the liver
  • the brain
  • the spine

The most common symptom of OWR is nosebleeds caused by telangiectasias in the nose. In fact, this is often the earliest symptom of OWR. Nosebleeds may happen daily or as rarely as twice per year.

When AVMs form in the lungs, they can affect lung function. A person with a lung AVM may develop shortness of breath. They may cough up blood. Serious complications from lung AVMs also include strokes and infections in the brain. People with OWR can develop these complications because without capillaries, blood clots and infections can travel directly from the rest of the body to the brain without a buffer.

A person with a gastrointestinal AVM may be prone to digestive problems, such as bloody stools. These are not generally painful. However, a loss of blood often leads to anemia. Gastrointestinal AVMs can occur in the stomach, intestines, or esophagus.

AVMs can be particularly dangerous when they occur in the brain. When one bleeds, it can cause seizures and minor strokes.

People with OWR inherit an abnormal gene that causes their blood vessels to form incorrectly. OWR is an autosomal dominant disorder. This means that only one parent needs to have the abnormal gene to pass it on to their children. OWR doesn’t skip a generation. However, the signs and symptoms may vary greatly between family members. If you have OWR, it’s possible that your child could have a milder or more severe course than you.

In very rare cases, a child can be born with OWR even when neither parent has the syndrome. This happens when one of the genes that cause OWR mutates in an egg or sperm cell.

The presence of telangiectasias is one indication of OWR. Other clues that might lead to a diagnosis include:

  • frequent nosebleeds
  • anemia
  • bloody stools
  • having a parent with the syndrome

If you have OWR, your doctor might want to do additional tests. For example:

  • A blood test can check for anemia, or iron deficiency in the blood.
  • A CT scan can show internal AVMs, such as in the lungs, liver, and brain.
  • A gastrointestinal doctor can insert a small camera down your throat to check for AVMs in your esophagus. This is called endoscopy.
  • An echocardiogram uses sound waves to check blood flow in and out of your heart.

If you have OWR, you should be screened for AVMs in the lungs and brain. This can help your doctor detect a potentially dangerous problem before something goes wrong. An MRI can screen for problems in the brain. CT scans can detect lung AVMs.

Your doctor can monitor the ongoing symptoms of this syndrome through regular checkups.

Genetic testing isn’t usually needed to diagnose OWR. These tests are expensive and may not be available in all circumstances. People with a family history of OWR who are interested in genetic testing should discuss their options with a genetic counselor.

The various symptoms of OWR each require their own types of treatment.


Nosebleeds are one of the most common manifestations of OWR. Fortunately, there are several types of treatments that may help. Noninvasive treatments include:

  • using a humidifier to keep the air in your home or workplace moist
  • keeping the inside of your nose lubricated with ointment
  • taking estrogen to potentially decrease bleeding episodes

If noninvasive remedies fail, there are other options. Laser therapy heats and seals the edges of each telangiectasia. However, you may need to have repeated sessions for lasting symptom relief. Septal dermoplasty is also an option for people with severe nosebleeds. The goal of this procedure is to replace the mucous membrane, or the thin lining of the nose, with a skin graft that provides a thicker lining. This cuts down on nosebleeds.

Internal AVMs

More serious surgery may be required for AVMs in the lungs or brain. The goal is to take preemptive action before there are problems. Embolization is a surgical process that treats lung AVMs by stopping blood flow to these abnormal blood vessels. It can be done in a few hours as outpatient surgery. This procedure involves the insertion of a material, such as a metallic coil, plug or glue, into the AVM in order to block it off. Surgery is required for brain AVMs and depends on their size and location.

Embolization is much trickier to perform on the liver. It can cause serious complications. Therefore, treatment for liver AVMs is targeted towards symptom improvement. If medical management fails, a person with OWR requires a liver transplant.


If intestinal bleeding causes anemia, your doctor will recommend iron replacement therapy. This will be in pill form unless you’re not absorbing enough iron. In that case, you may have to take iron intravenously. In serious cases, your doctor might order hormonal treatment or a blood transfusion.

Skin Symptoms

Dermatologists can treat port-wine marks with laser therapy if they bleed a lot or you dislike the way they look.

Other Complications of ORW Syndrome

When mouth bacteria enter the bloodstream and pass through a lung AVM, it can cause a brain abscess. An abscess is a collection of infected material containing immune cells and pus. This most often happens during dental procedures. If you have lung AVMs or haven’t yet been screened, talk to your doctor about taking antibiotics before proceeding with any dental work.

Most people with OWR lead perfectly normal lives. The syndrome is only life-threatening when an internal AVM begins to bleed uncontrollably. Visit your doctor regularly, so that they can monitor any internal AVMs.