4th June 2025

Aetiology

The majority of HHT cases are caused by a mutation in one of two genes involved in blood vessel development: activin receptor-like kinase 1 gene (chromosome 12) or the endoglin gene (chromosome 9). This mutated gene (inherited in an autosomal dominant pattern) produces abnormal blood vessels without the usual capillaries between arteries and veins (arteriovenous malformations – AVM). When small these are described as telangiectasia (telangiectases – plural), when large arteries and veins are involved they are called AVMs. AVMs are weak and have an increased risk of bleeding.

In HHT, patients will often present with epistaxis due to AVMs within the nose. They can often be spontaneous or after light trauma, however the severity of bleeding may vary hugely between different patients.

Telangiectases on the mucous membranes, lips, and face produce the most characteristic skin signs of HHT.