Targeted disruption of the murine Cdkn1b gene causes a gene dose-dependent increase in animal size without other gross morphologic abnormalities [11], and deletion of Pten in the hematopoietic compartment in mice promotes excessive proliferation of leukemogenic stem cells resulting in the development of myeloproliferative neoplasm (MPN) followed by acute leukemia [12]. This evidence concerns the gene CDKN1B and myeloproliferative disorder.