This research study is about understanding the risk of brain bleeding in people with a rare condition called Hereditary Hemorrhagic Telangiectasia (HHT). HHT causes unusual blood vessel formations, including in the brain. These brain formations can sometimes lead to bleeding, known as intracranial hemorrhage (ICH). The study involves many research centers in North America working together to find out why some people with HHT have brain bleeding and others do not. This will help doctors provide better care for HHT patients in the future.

Participants in the study will be asked to provide health information and a small blood sample. The study will last for several years, and participants will have regular check-ins. The study is looking for people diagnosed with HHT, who can give informed consent. Participants will not need to follow any strict rules or treatments; it's mostly about sharing health information.

• The study lasts for five years with annual follow-ups.
• Participants will provide health information and may give a blood or saliva sample.
• Participants will not receive any treatment as part of the study.