Background：

This gene encodes a type I cell-surface receptor for the TGF-beta superfamily of ligands. It shares with other type I receptors a high degree of similarity in serine-threonine kinase subdomains， a glycine- and serine-rich region (called the GS domain) preceding the kinase domain， and a short C-terminal tail. The encoded protein， sometimes termed ALK1， shares similar domain structures with other closely related ALK or activin receptor-like kinase proteins that form a subfamily of receptor serine/threonine kinases. Mutations in this gene are associated with hemorrhagic telangiectasia type 2， also known as Rendu-Osler-Weber syndrome 2.