In murine fetal liver cells and patients’ erythroid cells of essential thrombocythemia patients, ID1 expression is positively correlated with JAK2V617F mutation and is transcriptionally regulated by JAK2-STAT5 pathway to promote the erythroblast expansion and survival, and hence involved in the pathogenesis of erythrocytosis (Fig. 5) [20]. Here, JAK2 is linked to essential thrombocythemia.