Among patients with a MYH9 mutation, a limited number will be recruited in a second step for participating to specific studies focused on the consequences of MYH9 mutations on the proplatelets production and the platelet proteome. The selected patients should be representative of the different phenotypes of MYH9 syndrome. They should be adults and have a platelet count above 50 G / L. A blood sample will be drawn for this purpose during a second visit (V2).