GPS characterization and pedigrees. (A) Wright-Giemsa staining of blood smears demonstrates the large size and gray appearance of platelets in the affected person (left panel arrow) compared with her unaffected mother (right panel arrow). (B) Electron microscopy demonstrates the lack of α-granules in a platelet from the same person with GPS (left panel) compared with her mother (right panel). (C) Pedigrees for the 3 families that were analyzed in this study. Families 2 and 3 are Native American from a single settlement. Person 1 from family 1 is of Pakistani origin.