[Congenital amegakaryocytic thrombocytopenia (CAMT) - a defect of the thrombopoietin receptor c-Mpl]

Congenital amegakaryocytic thrombocytopenia with severe neurological findings

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare autosomal recessive disorder characterized by thrombocytopenia from failure of megakaryopoiesis. The genetic background of CAMT is mutations in the myeloproliferative ligand gene encoding the thrombopoietin receptor. In our patient with CAMT, we identified homozygous missense mutations [c.407C>T (p.P136L)]. The association of CAMT and central nervous system (CNS) abnormalities is uncommon. Here we present a case in which CAMT appears linked to CNS abnormalities (encephalomalacia, global atrophy) and developmental delay related with intrauterine intracranial hemorrhage.

CAMT in a female with developmental delay, facial malformations and central nervous system anomalies

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disorder characterized by thrombocytopenia and absence or decline in the number of megakaryocytic precursors in the bone marrow. It is caused by mutations in the thrombopoietin receptor gene, c-mpl, involved in the proliferation and differentiation of megakaryocytes and platelets. The association between CAMT and central nervous system (CNS) anomalies has been reported in the literature, albeit not very frequently. Here we present a unique case where CAMT appeared associated to cerebellum agenesis, hypoplasia of the corpus callosum and brainstem, facial malformations, and developmental delay.

Thrombopoietin Enhances Generation of CD34+ Cells from Human Embryonic Stem Cells

The role of thrombopoietin (TPO) in adult hematopoiesis is well-established. A recent report suggests that TPO and vascular endothelial growth factor (VEGF) play a role in promoting formation of early erythropoietic progenitors in a nonhuman primate embryonic stem cell (ES) model. No such report exists for human ES cells as yet. Because TPO may become an important factor promoting human ES cell-derived hematopoiesis, we sought to investigate whether TPO in combination with VEGF can enhance human ES-derived hematopoiesis in an EB-derived culture system. The emphasis of this work was to demonstrate the molecular mechanisms involved in this process, specifically the role of c-mpl and its ligand TPO. Human ES cells were cultured to the EB state, and EB-derived secondary cultures supporting hematopoietic differentiation were established: condition 1, control (stem cell factor [SCF] and Flt3 ligand [Flt3L]); condition 2, SCF, Flt3L, and TPO; and condition 3, SCF, Flt3L, TPO, and VEGF. Cells were harvested daily, starting at day 2 and continuing until day 8, for reverse transcription-polymerase chain reaction and Western blot. There was no evidence of expression of c-mpl and VEGF receptor on the gene or protein level until day 8, when the formation of well-established hematopoietic colonies began. This correlated with the formation of CD34+/CD31- negative progenitors, mostly found in blast-forming units-erythroid-like colonies. We concluded that TPO and VEGF play an important synergistic role in the formation of early ES-derived hematopoietic progenitors that occurs through the c-mpl and VEGF receptors. Disclosure of potential conflicts of interest is found at the end of this article.