Osler-Weber-Rendu Syndrome (OWR), also known as Hereditary Hemorrhagic Telangiectasia (HHT), is an inherited condition affecting the blood vessels. It affects approximately one person out of 10,000, or about 1.2 million people throughout the world.
Causes of Osler-Weber-Rendu Syndrome
Osler-Weber-Rendu syndrome is a genetic disorder caused by an abnormality in either the endoglin gene (ENG) on chromosome 9, or the activin receptor-like kinase 1 gene (ALK1) on chromosome 12. Both of these genes are involved in blood vessel formation. A mutation in either of these genes will result in similar OWR symptoms. People suffering from the disorder generally only have an abnormality in one of the genes.
OWR syndrome has an autosomal dominant pattern of inheritance, meaning only one copy of the abnormal gene is necessary to cause the disease and to pass it on. Each child of an individual who has the disorder has a 50% chance of inheriting it. The vast majority of those affected have a family history of the disorder.
Symptoms of Osler-Weber-Rendu Syndrome
Most symptoms of OWR syndrome are due to abnormal formation of the capillaries, tiny vessels that normally connect arteries to veins. Abnormalities in capillary formation cause defects known as arteriovenous malformations (AVMs). These are fragile areas in the vessels that cause them to break easily. AVMs may occur on the surface of the skin or in the lungs, brain, liver, stomach or gastrointestinal tract. Symptoms of Osler-Weber-Rendu syndrome often begin to appear in affected people when they are between 10 and 20 years old, and increase with age. Here are some common symptoms:
- Telangiectasias, which are small AVMs that may appear on the skin as red spots on the face, hands, lips or inside the mouth. They are fragile and may bleed spontaneously or from minor trauma.
- Nosebleeds (epistaxis) usually begin to appear at around 12 years of age due to telangiectasias in the nose.
- Anemia can be caused by blood loss from frequent nosebleeds or bleeding from AVMs elsewhere in the body such as the gastrointestinal tract.
- Pulmonary AVMs cause bleeding in the lungs, increase the risk of bacterial infections by interfering with the normal filtering processes, cause low oxygen levels, migraine headaches, and possibly lead to stroke.
- Brain AVMs can cause headaches, seizures, paralysis or stroke.
- Liver AVMs can interfere with normal circulation and lead to a risk of heart failure.
- Gastrointestinal AVMs can cause significant loss of blood, leading to anemia.
Diagnosis and Treatment of Osler-Weber-Rendu Syndrome
OWR syndrome is usually diagnosed by observation of symptoms such as frequent nosebleeds and telagiectasias, and whether there is a family history of the disorder. Blood counts can detect anemia and monitor blood oxygen levels. Chest x-rays or EKGs can assess if lungs and heart are normal; ultrasound can be used to find AVMs in the stomach or liver; MRIs are used to look for AVMs in the brain. Gastrointestinal bleeding can be detected by stool samples.
Treatment varies depending on the severity of the condition. Mild cases may require no treatment at all. Treatment for more severe symptoms may include iron supplements for anemia or laser therapy to seal telangiectasias. Chronic bleeding from the GI tract may require endoscopy and treatment by laser therapy or cauterization of the AVMs. Pulmonary AVMs may be treated with embolization, a procedure in which a tube is inserted through a vein in the groin area and used to place a balloon in the lung to block the bleeding artery. Brain AVMs may be treated by surgery, embolization, or stereotactic radiosurgery, which uses a focused beam of radiation.
Other treatments include hormone therapy with estrogen, or aminocaproic acid which improves clotting. In cases of severe blood loss, blood transfusions may be necessary. Many people who have Osler-Weber-Rendu syndrome do not have severe symptoms, and require minimal treatment to manage the condition, but early screening and proper diagnosis are crucial.