RUNX1 and Thrombocytopenia: Conditional knock-out studies also show a fundamental role for RUNX1 in megakaryopoiesis, with a marked decrease in polyploidization and cytoplasmic development of MKs, similar to what is observed for Gata1. The complex role of RUNX1 in MK differentiation is further illustrated by the autosomal dominant human syndrome familial platelet disorder with propensity to develop acute myeloid leukemia (FDP/AML), in which germline heterozygote RUNX1 mutations lead not only to thrombocytopenia, but also to impaired platelet function.