Thrombopoietin in thrombocytopenias of childhood.

This review summarizes the biology of thrombopoietin (TPO) in childhood. Studies on TPO and its receptor (c-mpl) have improved the understanding of inherited and acquired thrombocytopenias in childhood. Data are presented in this review regarding the molecular biology of TPO, differences in cellular effects on megakaryopoiesis, the regulation of TPO production, and TPO concentrations in health and disease. For neonatal thrombocytopenia, the focus is on early-onset thrombocytopenia associated with maternal diabetes, pregnancy-induced hypertension, intrauterine growth retardation, hypoxia, and sepsis. Fetal alloimmune thrombocytopenia allows insight into the biology of TPO when fetal megakaryopoiesis is chronically stimulated. In the thrombocytopenia absent radii syndrome and congenital amegakaryocytic thrombocytopenia, thrombocytopenia is caused by a disorder in the signal transduction at the c-mpl level and respectively directly on c-mpl. TPO concentrations in other inherited thrombocytopenias such as Fanconi anemia, Shwachman syndrome, Wiskott-Aldrich syndrome, and Bernard-Soulier syndrome are discussed. For acquired thrombocytopenias, data on TPO in aplastic anemia, immune thrombocytopenia, human immunodeficiency virus infection, and liver disease are given. Possible indications for a treatment with recombinant TPO in childhood are discussed, but the criteria to identify patients who would benefit need detailed evaluation.