TPO and congenital amegakaryocytic thrombocytopenia 1: In humans, TPO mutations that result in enhanced protein translation result in autosomal dominant thrombocytosis (elevated platelet count) (13–18), while loss-of-function mutations in TPO (or in its receptor MPL) result in congenital amegakaryocytic thrombocytopenia, a disease characterized by thrombocytopenia and absence of BM MKs at birth, with subsequent BM aplasia/failure later in life (19–26).