Hereditary Haemorrhagic Telangiectasia (HHT, also known as Osler-Weber-Rendu Syndrome) is an inherited vascular disease that leads to the development of dilated and fragile blood vessels. The study goal is to culture white blood cells that express the proteins mutated in HHT and examine in the laboratory to explain aspects of the HHT disease phenotype.

HHT is a vascular condition but many of the genes that are mutated to cause HHT (endoglin, ALK-1 and SMAD4) are also expressed in white blood cells. In this study, investigators will take blood samples from people with HHT, culture the white blood cells and study their properties in media prompting different types of differentiation, or infection of cell lines with Epstein Barr virus to provide cell lines which can be repeatedly studied. RNA and proteins will be extracted from these cells for study of white cell responses and association with expression levels of endoglin, ALK-1 and SMAD4. The investigators hypothesize that these cells which express "half-normal" endoglin, ALK-1 or SMAD4 will show differences when compared to normal white blood cells. It is also anticipated that that these findings may help to explain aspects of the HHT disease phenotype.

Inclusion Criteria:

• Patients with HHT,
• HHT patients family members

Exclusion Criteria:

• Unable to provide informed consent

Patients with hereditary hemorrhagic telangiectasia (HHT) and controls