What Is Hereditary Hemorrhagic Telangiectasia (HHT)?
Hereditary hemorrhagic telangiectasia, also known as Osler-Weber-Rendu syndrome or HHT, is a rare genetic disorder that affects blood vessels throughout the body. It is characterized by the formation of abnormal blood vessels, called telangiectases, which are fragile and prone to bleeding.
HHT can affect various organs, including the nose, lungs, brain, and gastrointestinal tract. It can cause a range of symptoms, from frequent nosebleeds to life-threatening complications. It is important to understand the causes, symptoms, and available treatment options for HHT to manage this condition effectively.
In the normal circulatory system, arteries take oxygenated blood from the heart and push it out to all parts of the body under high pressure, while veins return the blood back to the heart. Small capillaries typically connect the arteries to the veins. A person with HHT lacks capillaries in a few blood vessels in critical locations resulting in arteries that connect directly into veins. This creates a fragile vessel (telangiectasia) that can bleed or cause other problems.
Abnormal blood vessels in HHT patients are called:
- Telangiectases if they involve small blood vessels (nose, stomach, and intestine)
- Arteriovenous malformations (AVMs) if they involve a larger blood vessel (lung, brain, and liver).
Hereditary Hemorrhagic Telangiectasia Causes
In the mid-1990s scientists discovered that an abnormal gene on either chromosome 9 or 12 causes HHT. Chromosome 9 (endoglin, HHT-1) and chromosome 12 (activin-like kinase, HHT-2) tell the body to produce a substance that is involved in the formation of blood vessels. There are at least three other abnormal genes that can cause HHT.
HHT is a "dominant" disorder since one abnormal copy of the gene from one parent can cause the disorder. Although there is a 50 percent chance of inheriting this abnormal gene, children who do not have it cannot pass on the disease.
What Are the Symptoms of HHT?
The location of the telangiectases or AVMs impacts what problems a person with HHT might develop. Common symptoms of HHT include:
- Headaches or migraines
- Iron deficiency anemia
- Nosebleeds
- Seizures
- Shortness of breath
- Tiny, abnormal blood vessels on the hands, fingertips, face, lips, and nose
The most common symptom of HHT by far is nosebleeds, affecting about 90 percent of people with HHT. These can happen daily and often first occur in childhood.
Those with abnormal GI tract blood vessels should watch for dark stools or blood in the stool. Nosebleeds and bleeding into the intestine can cause severe anemia resulting in fatigue, shortness of breath, chest pain, and light-headedness.
Those with AVMs in the lung (called pulmonary AVMs or PAVMs) may be short of breath at rest or with exercise. They also may develop stroke or mini-stroke (TIA), heart attack, or an unusual infection, such as brain abscess. Rarely, PAVMs can rupture and cause bleeding in the chest (especially during pregnancy) or coughing up blood.
HHT patients with brain AVMs (also called cerebral AVMs or CAVMs) often do not have warning signs before a life-threatening brain hemorrhage. Heart failure is another risk HHT patients face due to high-flow liver AVMs (also called hepatic AVMs or HAVMs). These patients can also develop liver or bile duct problems.
How Does HHT Affect Women and Pregnancy?
Female hormones are known to affect bleeding of abnormal HHT blood vessels. For some people, nosebleeds vary through the menstrual cycle and become worse after menopause. Most pregnant people with HHT can expect no serious HHT-related complications, although they will generally be classified as high-risk. For some, new skin telangiectases are detected, while others report improvements.
How Is HHT Diagnosed?
Hereditary hemorrhagic telangiectasia can be diagnosed through genetic testing of a gene mutation or by using clinical criteria based on the signs and history of symptoms.
Genetic testing and diagnosis for HHT is available at Penn Hematology. Genetic testing can be extremely helpful in screening large families, in particular family members who have no signs or symptoms of HHT.
Diagnosis can be made if a person has three or more of the following criteria and HHT is suspected if they have two of the criteria:
- Nosebleeds that are spontaneous and recurrent
- Telangiectases are prevalent at characteristic sites, such as lips, oral cavity, fingers, and nose
- AVMs are present in lung, brain, GI, liver, or spine
- Family history indicates that a parent, sibling, or child has HHT
HHT Treatment at Penn Medicine
Interventional radiologists are one of the few specialists who can permanently treat hereditary hemorrhagic telangiectasia that affects approximately half a million people worldwide. As vascular experts, our Interventional Radiology Program performs embolization for PAVMs and telangiectasia, blocking the blood flow to the affected area to prevent symptoms and complications.
The University of Pennsylvania Hereditary Hemorrhagic Telangiectasia (HHT) Center of Excellence is directed by Dr. Scott Trerotola, and is a multidisciplinary practice. The center facilitates the comprehensive coordination of care necessary for treating HHT patients, including the full array of counseling, screening, diagnosis, and treatment.
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