<prompt> Intravascular hemolysis occurs in:Hereditary spherocytosisAutoimmune haemolytic anemiaParoxysmal nocturnal hemoglobinuriaThalassemia  <response>: PNH is a disease that results from acquired mutations in the phosphatidylinositol glycan complementation group A gene PIGA, an enzyme that is essential for the synthesis of certain cell surface proteins.Red cells, platelets, and granulocytes deficient in these GPI-linked factors are abnormally susceptible to lysis by complement. In red cells, this manifests as intravascular hemolysis, caused by the C5b-C9 membrane attack complex. The triad of hemolysis, pancytopenia and thrombosis is unique to PNH.Thrombosis is the leading cause of disease-related death in PNH.PNH is best made with flow cytometry in which there is presence of bimodal distribution of the red cells. 