Normal postnatal HgbA is composed of two α and β polypepide chains. In β – thalassemia there is a partial or complete deficiency in the synthesis of the β chain of the hemoglobin molecule. Consequently there is a compensatory increase in the synthesis of α chains, and ᵧ-chain production remains activated, which results in formation of defective hemoglobin. This unbalanced polypeptide unit is very unstable; when it disintegrates, it damages the RBCs, which causes severe anemia. To compensate for the hemolytic process, an overabundance of erythrocytes, is formed unless the bone marrow is suppressed by transfusion therapy. Excess iron from packed RBC transfusions and from the rapid destruction of defective cell is stored in various organs (hemosiderosis).