Both the constitutive thpo−/− and mpl−/− knockout (KO) mice and the conditional jak2 KO mice induced in adulthood after crossing them with transgenic mice expressing tamoxifen-inducible Cre under SCL promoter showed marked alterations in the HSC compartment associated with a thrombocytopenia (150–400 × 109/L) (26–28). This evidence concerns the gene JAK2 and Thrombocytopenia.