ITGB3 and Glanzmann thrombasthenia 1: Glanzmanns thrombasthenia (GT) is a rare (1: 200,000) congenital autosomal recessive bleeding disorder caused by either lack or dysfunction of the platelet integrin αIIbβ3, encoded by genes ITGA2B and ITGB3. The integrin serves as a receptor for fibrinogen and von Willebrand factor along with some other plasma glycoproteins.