Hereditary hemorrhagic telangiectasia: Abbreviated HHT. A genetic disease characterized by the presence of arteriovenous malformations (AVMs) which involve direct connections between arteries and veins without the usual intervening capillaries. These AVMs can vary in size from a pinhead to a pea. The tiniest AVMs are called telangiectases. Those telangiectases that are close to the surface of skin and mucous membranes tend to rupture easily and bleed after even slight trauma. Recurrent nosebleeds are common, particularly at night, beginning at about the age of 12, due to the rupture of telangiectases within the nose. Large AVMs can bleed in the gastrointestinal (GI) tract, brain, spine, lung, liver and other sites and create major, sometimes life-threatening, problems.
HHT is inherited as an autosomal dominant trait. Most patients with HHT have a parent with the disease. Every child born to a person with HHT has a 50% risk of inheriting their affected parent's mutation and having the disease. HHT can be caused by mutation in one of two different genes: the endoglin gene (ENG) on chromosome 9 or the activin receptor gene (ACTRL1) on chromosome 12. HHT has been genetically subdivided into HHT1 (due to ENG mutation) and HHT2 (due to ACTRL1 mutation). Some families with HHT may also have mutations in another, as yet unidentified, gene.
HHT is also known as Osler-Rendu-Weber and Rendu- Osler-Weber disease or syndrome. Although his name was never given to the disorder, it was first described in 1865 by the British physician Benjamin Guy Babbington (who also invented the laryngoscope).