Osler-Weber-Rendu syndrome

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Osler-Weber-Rendu syndrome


Osler-Weber-Rendu syndrome (OWR), or hereditary hemorrhagic telangiectasia (HHT), is a blood vessel disorder, typically involving recurrent nosebleeds and telangiectases (arteriovenous malformations that result in small red spots on the skin) of the lips, mouth, fingers, and nose. Arteriovenous malformations (AVMs) are abnormal, direct connections between the arteries and veins (blood vessels), causing improper blood flow. AVMs are often present in OWR, and may occur in the lungs, stomach, or brain.


The story of OWR began years ago with a sequence of events between three prominent physicians, Osler, Weber, and Rendu. The earliest report of OWR was compiled by Rendu in 1896. Osler further characterized the condition in 1901, and F. Parkes Weber described many cases of the vascular problems as well. OWR is caused by a genetic defect in the development of blood capillaries. Capillaries are vessels that exist between arteries and veins, connecting them throughout the body. The abnormality causes the capillaries to end bluntly, so they cannot properly connect the arteries and veins. Because of this, AVMs and telangiectases may result in various parts of the body.

Telangiectases on the skin represent a small AVM that has reached the outer surface of skin. Telangiectases usually have thin walls and are quite fragile, so they may burst spontaneously, causing bleeding. This bleeding may occur in the nose, explaining the frequent nosebleeds that result from little trauma. Telangiectases most often occur on the cheeks, lips, tongue, fingers, mouth, and toes. Occasionally, larger AVMs may exist in the brain, lungs, or stomach and this may lead to more serious bleeding. It is very rare for an individual to have all the symptoms typically found in OWR.

People with OWR do not have any mental limitations, and therefore have the same academic potential as anyone else. Nosebleeds may begin by age twelve, and may be initially assumed to be a typical childhood experience. However, if fatigue and other symptoms of anemia accompany the nosebleeds, they can pose great stress on a young child. Children with OWR may find it difficult if they play with and are unable to keep up with their peers. OWR has the potential need for continual medical management into adulthood, which can also be quite taxing on the individual and his or her family.

Genetic profile

OWR may be divided into two groups, OWR1 and OWR2. OWR1 is caused by alterations in the endoglin (ENG) gene , located on the q (long) arm of chromosome 9 at band (location) 34. AVMs of the lung may be more common in OWR1 than OWR2. OWR2 is caused by alterations in the activin receptor-like kinase 1 gene (ALK1), located on the q arm of chromosome 12 at band 1. Normally, ENG and ALK1 make proteins that are important in blood vessel formation. Therefore, alterations within these genes would naturally cause problems with blood vessels. The causes of OWR are complex; various alterations in multiple genes, or various alterations within the same gene, generate similar symptoms.

OWR is inherited in an autosomal dominant manner. An affected individual has one copy of an alteration that causes OWR. The individual has a 50% chance to pass the alteration on to each of his or her children, regardless of that child's gender. As of 2000, nearly all affected people have a family history of OWR, which is typically a parent with the condition.


As of 2000, OWR affects about one in 10,000 people. It spans the globe, but a higher prevalence exists in the Danish island of Fyn, the Dutch Antilles, and parts of France. It affects both males and females.

Signs and symptoms

The symptoms in OWR result from several AVMs, which may occur in differing severity and areas of the body. Ultimately, AVMs may lead to mild or severe bleeding in affected areas. As of 1998, about 90% of people with OWR experience frequent nosebleeds. They occur because the layers of mucous membranes in the nose are very sensitive and fragile, and AVMs in this area can easily and spontaneously bleed. Consistent nosebleeds may begin by about twelve years of age, and are not always severe enough to result in medical treatment or consultation. Occasionally, severe nosebleeds can cause mild to severe anemia, sometimes requiring a blood transfusion or iron replacement therapy.

Small AVMs, called telangiectases, commonly occur on the nose, lips, tongue, mouth, and fingers. They may vary in size from a pinpoint to a small pea. Because telangiectases are fragile, sudden bleeding may occur from only slight trauma, and bleeding may not spontaneously stop. Thirty percent of people with OWR report telangiectases first appearing before age 20, and 67% before age 40. Telangiectases and larger AVMs can be found anywhere in the gastrointestinal system, and if large enough they may cause a significant amount of internal bleeding. This bleeding may become more severe with age, but usually does not appear until age forty.

Pulmonary AVMs (AVMs of the lung) may cause bleeding within the lungs. As of 1998, this occurs in about 20% of people with OWR. These are problematic because the abnormal connections between arteries and veins bypass the natural filtering system within the lung, allowing bacteria to enter the system. Low levels of oxygen and infection may result, causing migraine-like headaches. An individual with a pulmonary AVM may experience intolerance to exercise, or may have areas of their skin turn blue (due to low oxygen levels). Complications in the brain may also result, sometimes causing a stroke. Occasionally, AVMs may occur in the spine, liver, and brain. A network of AVMs in the liver can cause blood to be forced away from the normal circulation, increasing the risk of heart failure because the heart becomes overloaded with blood.


As of 2001, genetic testing is available for OWR, but only on a research basis. The University of Utah offers linkage analysis to determine alterations in either ENG or ALK1, and results are not guaranteed. Linkage analysis is a method of genetic testing that requires several family members, both affected and unaffected, to give a blood sample for DNA analysis. The testing attempts to study family markers on the various chromosomes , in an attempt to find alterations near the proposed gene location. Results are abnormal if an alteration near ENG or ALK1 is found. If a familial alteration is identified, unaffected individuals could be offered testing to see whether or not they have the same alteration. If an individual had the alteration, he or she would be at risk for symptoms of OWR. Currently, no prenatal testing is available for OWR.

Because testing is neither widely available nor useful for diagnostic purposes, most people with OWR are identified by careful physical examination and study of their medical and family histories. Findings suggestive of an OWR diagnosis include nosebleeds (especially at night), multiple telangiectases (especially on the lips, mouth, fingers, and nose), and AVMs of various organs (especially the lungs, brain, liver, spine, and gastrointestinal (GI) tract). The final piece is a family history of OWR, with the affected person having the mentioned symptoms. OWR is considered definite when three or more findings are present, possible/suspected when two findings are present, and unlikely when fewer than two findings are present.

OWR is difficult to diagnose (and often under-diagnosed) because bleeding and venous malformations happen in otherwise healthy individuals. For example, isolated nosebleeds are very common in the general population and may occur for a variety of reasons. Because nosebleeds are often the first sign in OWR, they may initially be ignored, until they become so frequent that they are brought to medical attention. Isolated internal bleeding, or aneurysms, are quite common in the brain and GI tract. However, not all aneurysms are caused by AVMs and this needs to be determined, as AVMs are more specific to OWR. Most individuals with a pulmonary AVM actually have OWR.

Telangiectases may sometimes be a sign of other bleeding disorders, such as von Willebrand disease , a problem with blood coagulation (clotting). Telangiectases may also naturally occur in pregnancy or chronic liver disease. A hereditary form of telangiectases exists, and in this they are usually found on the face, upper limbs, and upper trunk of the body. Ataxia telangiectasia, another genetic condition involving telangiectases, should be considered if individuals have ataxia (problems with muscle coordination); movement and walking disorders are often observed with this condition as well.

Treatment and management

Treatment for OWR is based on the specific symptoms an individual experiences. To assess the need for treatment, a review of medical history regarding nosebleeds and other bleeding episodes should be noted. There should be careful inspection of any telangiectases. Stool samples may be analyzed to determine whether there is any blood present that is not obvious to the naked eye; this may indicate anemia. A complete blood count (CBC) can also determine whether anemia is a factor, due to blood loss. Pulse oximetry involves studying a blood sample, and determining whether the amount of oxygen absorption by red blood cells is normal. It can help to determine whether the lungs and heart are functioning properly, because their roles are to help oxygenate blood. Careful imaging of the heart by echocardiogram or chest x rays can assess whether the heart structures are normal. Chest x rays may identify pulmonary AVMs. Magnetic resonance imaging (MRI) of the head can visualize the brain to rule out any bleeding. An ultrasound of the liver and abdomen can help to rule out any AVMs in this area.

There are a few options for those who experience chronic nosebleeds. Generally, sterile sponges and sprays may help absorb free-flowing blood. Another option is laser therapy, used for individuals who have mild to moderate nosebleeds. A small laser beam is directed around each telangiectasis, and automatic clotting occurs, sealing them. It is usually done under local anesthesia, and few complications exist. Nearly everyone sees improvements for several months, and the procedure may be repeated as needed. For more severe cases (sometimes requiring transfusions) there is septal dermoplasty, first pioneered in the 1960s. This replaces the normally fragile lining of the nose with a tougher lining, using a skin graft from the thigh area. The procedure can be done with local or general anesthetic, and has minimal complications. Some individuals never have nosebleeds again after the operation, but most of them experience a significant lessening of symptoms. Estrogen and aminocaproic acid (an amino acid) therapies have also been found to help with clotting in the nose. Estrogen improves the smoothness of layers of skin on the telangiectases, making them less fragile. Aminocaproic acid improves the clotting process by magnifying the protein responsible for clotting.

Gastrointestinal bleeding is one of the most difficult symptoms of OWR to treat. Endoscopy can help to identify the location of the AVM. Using an endoscopic probe, treatment can be attempted by laser or through cauterization—sealing the injury with heat. These help to seal the telangiectasis or AVM. If bleeding is severe, iron therapy is often needed to help build more red blood cells and alleviate anemia. Hormone therapy (with estrogen and progesterone) has been helpful in many patients with chronic GI bleeding. As of 1998, no perfect treatment for liver AVMs has been established, but embolization therapy has been used. For more severe cases (usually in older individuals) liver transplant may be considered.

Pulmonary AVMs are often treated with a procedure known as balloon embolization. A small tube is inserted into a large vein in the groin. It is passed through the blood vessels to the pulmonary AVM. A balloon or coil is placed into the artery leading into the AVM, blocking it off completely, and this stops the bleeding. This usually takes 1–2 hours, with minimal recuperation time. Pulmonary AVMs can almost always be treated very well with this method. Women with OWR who become pregnant and have untreated pulmonary AVMs run a high risk for an internal lung bleed. They should be treated during their second trimester to avoid this complication. Pregnant women with treated pulmonary AVMs appear to be at no higher risk for bleeding than pregnant women without pulmonary AVMs.

For generalized anemia, iron replacement and red blood cell transfusions may become necessary. People with OWR may develop medical problems unrelated to the condition, such as ulcers or colon cancer, which may cause additional GI blood loss.

Because telangiectases can occur in the mouth, dental work may be a particular problem for those with OWR. Bleeding in the mouth makes the oral area susceptible to oral bacteria, such as those on the gums. Bacteria can enter the bloodstream and cause infections in other areas of the body. The best preventive measure for this is to take antibiotics before any dental work in order to prevent infection. Additionally, medications such as aspirin and non-steroidal anti-inflammatory agents (such as Advil, Aleve, and Motrin) should be avoided because they can increase bleeding.

Since effective treatment measures are available, unaffected at-risk individuals in a family should be screened for symptoms of OWR, especially for brain, pulmonary, and GI AVMs.


Prognosis for individuals with OWR is good, assuming they receive appropriate and timely treatments. Because many treatments are effective, proper screening is crucial to prognosis.



Christensen, Gordon J. "Nosebleeds may mean something much more serious: an introduction to HHT" Journal of the American Dental Association 129, no. 5 (May 1998): 635–37.

Garcia-Tsao, Guadalupe, et al. "Liver disease in patients with hereditary hemorrhagic telangiectasia." The New England Journal of Medicine 343, no. 13 (September 28, 2000): 931–36.


HHT Foundation International, Inc. PO Box 8087, New Haven, CT 06530. (800) 448-6389 or (410) 584-7287. Canada: (604) 596-3418. Other countries: (914) 887-5844. Fax: (410) 584-7721 or (604) 596-0138. [email protected] <http://www.hht.org>.


Birth Disorder Information Directory. <http://www.bdid.com/owrs.htm>.

Family Village.<http://www.familyvillage.wisc.edu/lib_ht.htm>.

"Hereditary Hemorrhagic Telangiectasia (HHT) Syndrome." University of Michigan Health System.<http://www.med.umich.edu/1libr/topics/hemo03.htm>.

Deepti Babu, MS