The discovery of mutations in ANKRD26, RUNX1, and the ETS family transcription factors has led to an increased understanding of the genetic basis of hereditary syndromes involving thrombocytopenia, red cell macrocytosis and leukemia [9,10,17,18] and of the pathways regulated by these genes [17,45]. The gene discussed is RUNX1; the disease is Thrombocytopenia.