Hereditary hemorrhagic telangiectasia, also known as HHT or Osler-Weber-Rendu syndrome, is inherited as an autosomal dominant trait. Affected children develop red or reddish-purple collections of abnormal blood vessels called telangiectases (spider-like, macular, or papular spots).

The telangiectases can be seen on the lips and tongue and the nasal mucosa. Other areas such as the face and ears may be involved and internal vascular abnormalities can occur in the brain, lungs, throat and larynx, gastrointestinal tract, liver, bladder, and vagina.

Frequent nosebleeds in children may be an early sign but the easily visible, characteristic vascular lesions (telangiectases) on the tongue and lips may not appear until puberty. The telangiectases bleed easily. Bleeding into the head (brain hemorrhage, stroke) may cause varied neurological symptoms such as seizures. If severe, this brain hemorrhage may be fatal.

Some patients only discover that they have this condition when they cough up blood and a chest X-ray shows an abnormality called an arterio-venous malformation. Some patients have enough large or multiple arterio-venous malformations in the lungs to cause shortness of breath.