Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant genetic disorder of the blood vessels which affects approximately 1 in 5,000 people worldwide. Historically, HHT was known as Osler-Weber-Rendu syndrome, named after the doctors who first studied the disorder. The phenotype of HHT is wide-ranging, from very mildly affected patients who never know they have the disease to severely affected people who require significant treatment. The most common symptoms are nosebleeds and the presence of small arteriovenous malformations (AVMs), also known as telangiectases, on the nose, lips and tongue. Larger AVMs can occur in the brain, lung, liver or gastrointestinal tract, leading to more severe symptoms which usually require treatment to prevent persistent or life-threatening bleeding and other complications.

Various mutations in two genes, endoglin (ENG) and activin-like kinase 1 (ACVRL1) are responsible for HHT. The ENG gene resides on the long arm chromosome 9 and consists of 15 exons encoding a protein product of 658 amino acids. ACVRL1 is located on the long arm of chromosome 12, consisting of 9 coding exons which result in a shorter protein product of 503 amino acids. Normally, both the ENG and ACVRL1 protein products are involved in the formation of blood vessels. Mutations in either of these genes can disrupt this process and cause the malformation of blood vessels leading to the symptoms seen in HHT patients.

To find out about HHT in more detail, visit the the HHT Foundation International website.