This unexpected conclusion was later supported by (1) the finding of c-Mpl expression on primitive hematopoietic cells [43]; (2) the fact that genetic elimination of c-Mpl or thrombopoietin in mice results in a 7–8-fold reduction in transplantable HSCs [44]; and (3) “experiments of nature”; genetic mutation or elimination of thrombopoietin, or more commonly of c-Mpl, in humans leads not only to greatly reduced numbers of megakaryocytes and platelets (an inherited disorder termed amegakaryocytic thrombocytopenia), but also to aplastic anemia in affected children [45,46]. This evidence concerns the gene THPO and idiopathic aplastic anemia.