GALE-mediated glycosylation in megakaryocytes and platelets. During late stages of megakaryopoiesis, GALE induces GPIbα and β1 integrin glycosylation in the ER, thereby leading to the trafficking of GPIb-IX-V complex and β1 integrin onto the megakaryocyte surface and subsequently onto newborn platelets. Normal glycosylation supports the interactions between FLNA and GPIbα in the plasma membrane and connects the actin cytoskeleton to the GPIbα complex. In contrast, decreased protein levels and/or reduced enzymatic activity of GALE leads to GPIbα and β1 integrin hypoglycosylation, retaining them in the ER and reducing their externalization on the cell surface. Impaired GALE function also leads to the disorganized and nonuniform actin cytoskeleton and delocalization of FLNA and actin from the plasma membrane to the cytoplasm, forming actin patches, thereby reducing actin contractility. These pathologic processes strongly impair platelet production, size, and function. Therefore, GALE mutant-patients develop macrothrombocytopenia, characterized by giant/gray and apoptotic platelets with strongly reduced membrane localization of GPIb-IX-V complex and β1 integrin, defective granule secretion, and platelet aggregation. GP, glycoprotein; FLNA, filamin A.