[Paroxysmal nocturnal hemoglobinuria--consequences of a missing anchor]

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hematological disorder characterized by the clonal expansion and differentiation of a multi-potent hematopoietic stem cell carrying a somatic mutation in the X-linked PIG-A gene. As a consequence of this mutation, glycosylphosphatidylinositol (GPI)-anchored proteins are lacking on the surface of blood cells derived from the mutated stem cell. This may result clinically in hemolytic anemia and a tendency for venous thrombosis and serious infection. Bone marrow failure is a frequently observed phenomenon associated with PNH. Reliable diagnosis of PNH is currently best achieved by flow cytometric analysis of GPI-anchored proteins on peripheral blood cells. Both the clinically relevant size of the PNH clone and type of GPI deficiency (complete or partial) can be reproducibly determined by this method. Most patients will benefit from supportive measures, albeit that allogeneic hematopoietic stem cell transplantation is currently considered the only potentially curative therapy. The development of a new therapeutic monoclonal antibody that reduces intravascular hemolysis and progress in diagnostic flow cytometry using a new GPI-specific marker may provide further benefit for PNH patients in the future.