Blood platelets are small cell particles that are essential for blood clotting and hence prevent excessive bleedings. Patients with a defect in platelet formation suffer from bleedings. Vice versa, patients with elevated platelets are at risk for blood clotting that could block blood supply to major organs. These serious health problems underscore the importance of balanced platelet formation. One crucial protein that regulates the growth of platelet-producing cells and platelet levels is MPL. My preliminary data strongly suggests an essential role for the sugar modification “C-mannosylation” in MPL function. I propose to decipher how C-mannosylation influences MPL function and platelet production. Additionally, I will uncover C-mannosylation disturbances in patients with too few or too many platelets. Knowledge on this vastly unexplored topic can then be exploited for therapeutic purposes and to improve in vitro platelet production for transfusions.