Schematic representation showing the spectrum of missense mutations that give rise to GT. From a survey of the literature and on consulting the GT database (http://sinaicentral.mssm.edu/intranet/research/glanzmann), a total of 113 different ITGA2B mutations include 54 missense mutations that distribute across the 30 exons (red bars) of the gene (A), whereas the 72 reported ITGB3 mutations include 44 missense mutations distributed across 15 exons (B). The defects (in single letter amino acid code) responsible for lack-of function variant forms are in black; blue, those that primarily prevent αIIbβ3 expression; green, mutations characteristic of ethnic groups; orange, the substitutions give activated integrin; and rose, GT is associated with macrothrombocytopenia. Asterisks indicate the number of times the defect has been reported in apparently unrelated families. Amino acid substitutions that give rise to human platelet alloantigen systems without affecting αIIbβ3 expression or function are shown in boxes. Mutations giving rise to GT are distributed across both genes. In contrast, variant forms are more likely to have β3 gene defects (see also Table 1).