Everything you need to know about nosebleeds, arteriovenous malformations, and other symptoms of HHT. Hereditary Hemorrhagic Telangiectasia (HHT) is a rare genetic disorder that causes blood vessel abnormalities in the nose, skin, gastrointestinal tract, lungs, brain, and liver. Nosebleeds are the most common symptom of HHT, but abnormal vessels in other organs, if they are not diagnosed and treated, can lead to serious medical complications,...