Hereditary hemorrhagic telangiectasia
What is hereditary hemorrhagic telangiectasia?
Hereditary hemorrhagic telangiectasia (HHT) is a rare genetic disorder. This means that people have a problem in a specific gene. People have about 20,000-25,000 genes in their bodies. Genes are like our body's instruction manual - they control the growth, development and normal function of the body. Because of a change in one of at least four different genes, people with HHT lack a protein. These proteins are essential for the proper growth and develop of blood vessels. Usually, the arteries (the vessels that carry away from the heart) are connected to the veins (the vessels that carry blood to the heart) by very tiny blood vessels called capillaries. In HHT, the capillaries may not form properly and the arteries may be connected directly to the veins. These abnormal connections are called arteriovenous malformations (larger AVMs) or telangiectasia (small-sized AVMs), when they occur near the surface of the skin or mucous membranes. The site where these abnormal connections occur is fragile and can rupture easily, causing bleeding. The signs and symptoms can be very different in one person when compared to another. This is true even for people in the same family. Sometimes, symptoms are present in infancy, while other times people do not develop symptoms until well until adulthood. Some people have severe symptoms while others may have very mild ones. Chronic nosebleeds are a common symptom. They may occur spontaneously (without a cause). Usually, most people develop chronic nosebleeds during childhood or adolescence. Telangiectasia, which appear as small reddish lesions, may form on lips, tongue, face, chest, fingers, or mucous membrane that lines the inside of the cheeks. AVMs usually affect the liver, lungs or brain. Some people have severe symptoms while others may have very mild ones. HHT is usually caused by alterations (mutations) in one of four different genes, called ACVRL1, ENG, GDF2, or SMAD4.
Hereditary hemorrhagic telangiectasia. Genetics Home Reference website. Accessed February 23, 2017. https://ghr.nlm.nih.gov/condition/hereditary-hemorrhagic-telangiectasia
McDonald J, Pyeritz RE. Hereditary Hemorrhagic Telangiectasia. GeneReviews website. Accessed February 23, 2017. https://www.ncbi.nlm.nih.gov/books/NBK1351/
Hereditary hemorrhagic telangiectasia. The National Organization for Rare Disorders website. Accessed February 23, 2017. https://rarediseases.org/rare-diseases/hereditary-hemorrhagic-telangiectasia/