Hereditary hemorrhagic telangiectasia or HHT (also called Osler-Weber-Rendu syndrome) is a genetically linked disorder that causes abnormalities in the blood vessels. Patients can develop telangiectasia, which is an abnormal dilation or enlargement of the small blood vessels that can be seen on the skin surface.

They may develop an arteriovenous malformation (AVM) in lungs, brain, or liver. AVMs are a tangle of blood vessels that connect the arteries and veins. The development of these abnormal vessels can lead to a variety of symptoms such nosebleeds, gastrointestinal bleeding, and low blood counts.

Most people with HHT function normally, which is why the disorder often may go undiagnosed. If the brain or lungs are involved, it may severe complications may result.