MPL and Thrombocytopenia: In contrast, humans with total loss‐of‐function of MPL have congenital amegakaryocytic thrombocytopenia (CAMT) that involves severe thrombocytopenia due to impaired megakaryocyte production evolving to trilineage marrow aplasia within the first years of life (Ihara et al, 1999; Ballmaier & Germeshausen, 2009).