Hemolytic anemias due to hemoglobinopathies.

Hemoglobinopathies responsible for hemolytic anemias may be divided into two groups. The first one corresponds to thalassemias and the second to the presence of a structurally abnormal hemoglobin (Hb). In thalassemia, the primary biochemical abnormality is a quantitative defect in the biosynthesis of one type of Hb chain. This defect leads to an overall deficit of Hb accumulation in the erythrocyte (hypochromia) together with the presence of an excess of the normally synthesized chains. The unpaired subunits which are less soluble than HbA precipitate, bind to the membrane and ultimately lead to hemolysis. In the second group, the hemolytic anemia is a direct consequence of the physicochemical properties of the structurally abnormal Hb. This molecule may polymerize, precipitate or crystallize within the red blood cell (RBC) leading to membrane alterations and to the destruction of the cell. This chapter will emphasize several examples of structurally abnormal Hbs, such as sickle cell disease and congenital Heinz body hemolytic anemia (CHBHA).