Pathogenesis

To date, mutations in two genes have been linked to HHT, accounting for most but not all clinical cases. Mutations of the ENG gene, localized to the long arm of chromosome 9 (9q33-q34.1), cause HHT1; mutations of the gene encoding activin receptor-like kinase 1, ALK1 (also known as ACVRL1), localized on the long arm of chromosome 12 (12q11-q14), cause HHT2. It is not clear whether genotype-phenotype correlations can be established in HHT, but there may be a higher prevalence of pulmonary AVMs in HHT1.

ENG and ALK1 encode receptor proteins, which are members of the transforming growth factor-beta (TGF p) superfamily. Therefore, HHT is caused by a disturbance in the

TGF p signaling pathway, which is an important pathway involved in cellular proliferation, differentiation, adhesion, and migration. However, the exact mechanism of how a disturbance of this pathway leads to HHT remains unclear.

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