Hereditary hemorrhagic telangiectasia (HHT) is an inherited disorder that affects the blood vessels. A person with HHT may have blood vessels that have not developed properly and may have no capillaries.

Some people may also refer to HHT as Osler-Weber-Rendu syndrome.

HHT is a condition that can cause malformations of different blood vessels. HHT affects males and females equally, affecting approximately 1 in 5,000 people.

Symptoms of HHT can occur at any age and may vary between individuals. Common signs of HHT include frequent nosebleeds and visible red or purplish spots on the body.

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Blood vessels are the channels in the body that distribute blood. The main blood vessels are:

  • Arteries: Arteries carry oxygenated blood away from the heart and distribute it to the different areas of the body.
  • Capillaries: Capillaries are the smallest blood vessels. They connect the arteries to the veins. The main role of capillaries is the exchange of materials between the blood and other cells in the body.
  • Veins: Veins carry deoxygenated blood toward the heart after it has passed through the capillaries.

HHT is a genetic condition that affects the blood vessels. Specifically, it results in multiple telangiectasias throughout the body. These are small blood vessels that sit near the skin’s surface and widen and create visible patterns of lines.

HHT can cause malformations of blood vessels. It can also cause people to develop blood vessels without capillaries. These are tiny blood vessels that pass blood from arteries to veins.

If a person with HHT has no capillaries, the space between an artery and a vein may be very fragile. This can cause them to burst and bleed.

Blood vessel malformations associated with HHT can cause problems to develop in the:

  • lungs
  • brain
  • spinal cord
  • liver

The most common sign of HHT is frequent nosebleeds. This occurs due to a person having small and irregular blood vessels within the nose. These blood vessels may rupture easily and cause nosebleeds.

Another symptom of HHT is the presence of red or purplish spots on the skin. These spots tend to lighten briefly when a person touches them. These spots develop due to abnormal blood vessels in the skin. These spots can appear on the:

  • hands
  • fingertips
  • face
  • lips
  • mouth lining
  • nose

HHT can also cause abnormal blood vessels to develop inside the digestive tract. This can lead to bleeding in the stomach or intestines. Medical professionals refer to this as gastrointestinal (GI) bleeding.

Sometimes, HHT may cause people to develop abnormal connections between the arteries and veins in the:

  • brain
  • lungs
  • liver

These abnormal blood vessel connections may rupture, causing internal bleeding. They may display no warning signs before this happens.

HHT is a genetic disorder. Alterations in five different genes can cause HHT. These include:

  • ENG gene
  • ACVRL1 gene
  • SMAD4 gene
  • BMPR9 gene
  • RASA1 gene

Every person who has HHT has one gene variation that causes them to have the disorder.

If someone with HHT has a child, they have a 50% chance of inheriting the gene alteration. If this is the case, they will develop HHT.

In some rare cases, a person may develop HHT due to the result of a spontaneous genetic change. This is a new variation that they have not inherited from a parent.

A doctor may perform a clinical assessment and take a detailed family history if they suspect a person has HHT. Assessing the individual’s family history is important, as HHT is a genetic disorder.

An international group of HHT experts established four diagnostic criteria for HHT:

  1. Recurrent spontaneous nosebleeds.
  2. The presence of multiple small, widened blood vessels on the skin in certain locations.
  3. The presence of widened blood vessels inside the body.
  4. A family history of HHT.

If someone has at least three of the four criteria, a doctor can diagnose HHT.

A doctor can confirm their HHT diagnosis through genetic testing.

During genetic testing, a medical professional will take a person’s blood sample. They will then send this sample away for testing.

This testing can help determine whether the specific genetic mutations are present, helping diagnose HHT.

Many people with HHT develop a complication called arteriovenous malformations (AVMs). These occur when blood vessels form abnormally.

People with HHT often have AVMs that cause direct connections between blood vessels that do not usually connect. This commonly occurs in blood vessels in the:

  • lungs
  • brain
  • spinal cord
  • liver

Around 50% of people with HHT experience AVMs in their pulmonary blood vessels. Medical professionals refer to these as pulmonary AVMs (PAVMs).

PAVMs can cause complications, such as:

Other serious complications of PAVMs include brain abscesses and stroke. These may occur due to blood clots or bacteria passing through a PAVM.

If a person has AVMs that develop in their brain, it may result in complications, such as:

If AVMs develop in a person’s spinal cord, they can experience back pain and the loss of feeling or function in their arms and legs.

HHT can also cause GI bleeding to occur.

Bleeding episodes can increase in severity as people age. This can cause low levels of iron in the blood, which can lead to a person developing anemia due to a decreased red blood cell count.

Symptoms of anemia associated with HHT include:

  • chest pain
  • shortness of breath
  • fatigue

There is currently no cure for HHT. Treatment for HHT tends to depend on the symptoms a person experiences.

Treating nosebleeds and blood loss

If a person has regular nosebleeds or GI blood loss due to HHT, they can take iron supplements. This is to replace any iron they have lost from their blood due to these nosebleeds. People can also use nasal lubricants to help reduce nosebleeds. Laser treatments may also be an option.

If someone has more serious GI bleeding, they may require treatment with iron replacement therapy or blood transfusions.

A person with HHT may also take an intravenous antiangiogenic drug called bevacizumab, which can help reduce nosebleeds and anemia. It may also help prevent GI bleeding.

Treating AMVs

Medical professionals may suggest treatment if a person has AMVs. This treatment usually involves a procedure called embolization.

This involves blocking the blood supply to the AMVs by inserting a tiny plug inside the artery that supplies the abnormal blood vessels.

Doctors tend to prefer embolization to open surgery, and the procedure usually takes place under sedation.

If a person has AMVs in their brain, a doctor may suggest embolization or surgery to treat them. They may also use a procedure called stereotactic radiotherapy, which involves precisely delivering radiation to the affected blood vessel.

Medical professionals can also use certain types of specialist treatment to treat liver AVMs.

If a person has liver AVMs and they do not respond well to medical therapy, they may require a liver transplant.

HHT is an inherited disorder that can cause issues with certain blood vessels. Some people refer to HHT as Osler-Weber-Rendu syndrome. HHT can cause a person to develop abnormal connections between blood vessels.

Common symptoms of HHT include frequent nosebleeds and red or purplish spots on the body. HHT can also cause internal bleeding. There is currently no cure for HHT. Treatment usually involves treating the symptoms of the disorder.