This study will identify and characterize the gene or genes responsible for Gray Platelet syndrome (GPS). Platelets are small blood cells that stick on injured blood vessels to form a plug and stop bleeding. When a blood vessel is injured (like a cut on a finger), platelets release the proteins stored in their sacs to help form a blood clot. Patients with GPS bleed longer than other people because their platelets lack some of these protein-carrying sacs. Platelets without sacs look pale gray under the microscope rather than pink, giving the syndrome its name. Except for rare patients with severe hemorrhage, the bleeding tendency in GPS is usually mild to moderate, with patients experiencing easy bruising, nosebleeds, and, in women, excessive menstrual bleeding.

Patients with GPS and members of their family with GPS may be eligible for this study. Participants will provide a personal and family medical history and will have blood drawn. About 1 to 2 tablespoons of blood will be drawn in adults, and about 1 teaspoon in children. The blood will be analyzed for genes that cause GPS