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Hereditary Haemorrhagic Telangiectasia

HHT is a hereditary, autosomal dominant disease of the blood vessels, which means that children of HHT patients have a 50% chance of inheriting the disease.

Hereditary Haemorrhagic Telangiectasia (HHT or Rendu Osler Weber disease) is a relatively rare disease, and as a consequence, doctors often have little experience or knowledge of the disease. It is a complex disorder involving both a genetic susceptibility and other internal and external (environmental) factors. This site provides up-to-date information about HHT for patients, relatives and medical professionals who are involved with HHT. 

Arteriovenous malformation in hht versus a normal capillary network

The characteristic abnormality of the blood vessels is a dilation at the site of the capillaries. Normally, arteries divide many times into smaller arteries and end in the capillaries. These capillaries fuse again to form the veins. In HHT, we find dilations instead of capillaries at certain spots.

These abnormalities can occur anywhere in the body, since all the blood vessels are subject to the same hereditary deficiency. However, there are predilection sites, such as the skin on the face and fingers, and the mucous membranes of the nose, mouth and digestive tract. Usually, these involve small dilations of several millimetres, the so-called telangiectases. These bleed easily – e.g. as nose bleeds – because of their thin walls and superficial position. Other predilection sites are the lung, brain and liver. These usually involve larger abnormalities (up to 10 centimetres), the so-called arteriovenous malformations (AVMs). The AVMs tend to bleed less because they are protected by surrounding tissues. However, other symptoms may be present depending on which organ is affected.

More information on HHT symptoms and how they present themselves in different parts of the body.

Cause

HHT is a hereditary vascular disease caused by the shortage specific proteins which help stabilize blood vessel walls: "endoglin" or "activin-receptorlike-kinase-I (ALK-1)". The process of stabilizing blood vessel walls is especially important when blood vessels have to be repaired after injury. This explains why there are usually no symptoms of HHT at birth, but present and progress later in life.

Sunlight might be an example of such external injury. The dermal lesions are found particularly on the skin most exposed to the sun, such as the face and hands. What other factors also play a role in HHT isn't currently known. By conducting extensive scientific research we will gain more knowledge on this in the future.

DNA, mutations and heredity aspects

Our hereditary properties are anchored in the DNA of our genes. The cause of HHT is usually a change (mutation) in the genes responsible for the production of endoglin (chromosome 9) or ALK-1 (chromosome 12). Such a mutation is usually inherited from one of the parents, but it may also develop spontaneously.

HHT shows dominant inheritance and is not sex-linked. This means that both men and women equally affected and can pass it on to next generations. Each characteristic of a person’s body is represented by a pair of genes, one from the father and one from the mother. Dominant inheritance means that the mutated gene from one parent overrules the normal (not mutated) gene from the other.

More information regarding heredity and DNA in HHT

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