Primary polycythemias.

In this review, primary polycythemic states are discussed in the context of other polycythemic disorders. Primary polycythemias result from an acquired or inborn mutation affecting hematopoietic and erythroid cells. The best-known type of primary polycythemia is polycythemia vera, which is caused by an acquired somatic mutation of a hematopoietic stem cell with exaggerated myeloid proliferation; the molecular events leading to this disease are not understood. In contrast, primary familial and congenital polycythemias result from inborn mutation affecting hematopoietic and erythroid cells. The molecular mechanisms causing primary familial and congenital polycythemias may be different in different families; some have already been defined. Progress in defining the molecular defect of primary polycythemias and the better understanding of altered signal transduction leading to excessive erythrocyte production should provide important insights into the pathogenesis of primary polycythemias, other leukemic disorders, as well as normal hematopoiesis. Such information should contribute to better understanding of and more effective therapeutic interventions in myeloproliferative and leukemic disorders.