The GP1BB gene encodes the beta chain subunit of platelet glycoprotein Ib. Glycoprotein Ib (GP-Ib) is a protein complex found on the surface of platelets that plays a vital role in blood clotting. GP-Ib consists of two polypeptides – an alpha chain and a beta chain, and it forms the main portion of the GPIb-V-IX system, which functions as a receptor for von Willebrand factor (VWF) involved in normal platelet adhesion.
Mutations in GP1BB is associated with Bernard-Soulier syndrome and autosomal dominant macrothrombocytopenia. Mutations in GP1BB prevent the formation of the GP-Ib complex or affect its ability to interact with von Willebrand factor. This results in impairment of clot formation, leading to excessive bleeding seen in patients with Bernard-Soulier syndrome.