Hereditary Haemorrhagic Telangiectasia (HHT)

Hereditary Haemorrhagic Telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome, is a rare genetic disorder characterized by the formation of abnormal blood vessels, which can lead to bleeding and other complications.

Causes and Genetics

HHT is caused by mutations in one of several genes, including ENG, ACVRL1, SMAD4, and GDF2. These genes are responsible for the development and maintenance of blood vessels. The condition is inherited in an autosomal dominant pattern, meaning that a single copy of the mutated gene is enough to cause the disorder.

Symptoms

The symptoms of HHT can vary widely, but common features include:

• Telangiectasias: small, dilated blood vessels that appear as red spots on the skin and mucous membranes
• Epistaxis (nosebleeds): frequent and recurrent nosebleeds due to the presence of telangiectasias in the nasal passages
• Gastrointestinal bleeding: bleeding from the digestive tract, which can lead to iron deficiency anemia
• Avascular malformations (AVMs): abnormal connections between arteries and veins that can occur in various organs, including the brain, liver, and lungs
• Arteriovenous fistulas: abnormal connections between arteries and veins that can lead to heart problems and other complications

Diagnosis

The diagnosis of HHT is based on a combination of clinical evaluation, family history, and genetic testing. The following criteria are used to diagnose HHT:

• Epistaxis (nosebleeds)
• Telangiectasias
• Visceral AVMs (e.g., in the liver, lungs, or brain)
• Family history of HHT
• Genetic testing: identification of a mutation in one of the genes associated with HHT

Treatment and Management

The treatment and management of HHT depend on the severity and location of the symptoms. The following measures may be used:

• Iron supplementation: to treat iron deficiency anemia due to chronic bleeding
• Blood transfusions: to replace blood lost due to severe bleeding
• Embolization: a minimally invasive procedure to block abnormal blood vessels and prevent bleeding
• Surgery: to remove or repair AVMs and arteriovenous fistulas
• Laser therapy: to treat telangiectasias and reduce bleeding
• Bevacizumab (Avastin): a medication that can help reduce the size and number of telangiectasias

Complications

HHT can lead to several complications, including:

• Anemia: due to chronic bleeding
• Heart failure: due to the presence of AVMs and arteriovenous fistulas
• Stroke: due to the rupture of AVMs in the brain
• Pulmonary hypertension: high blood pressure in the lungs due to the presence of AVMs
• Liver disease: due to the presence of AVMs in the liver

Prognosis

The prognosis for individuals with HHT varies depending on the severity and location of the symptoms. With proper treatment and management, many people with HHT can lead active and normal lives. However, the condition can be life-threatening if left untreated or if complications arise.