This classification is based on the type of globin chain (alpha or beta) which is affected. This clearly indicates that hemoglobin structure is central to the pathology of thalassaemia. Beta thalassaemia or Cooley's anemia as it is called refers to decreased beta chain production and hence deficits in hemoglobin due to defects in the gene forming the chain
Hemoglobin (Hb) is protein responsible for oxygen carrying in the body. It is made of four peptide chains, two alpha or a chains and two beta or b chains. Hemoglobin synthesis is controlled by genes which are switched on and off at different phases in the human life (beginning at the embryonic stage). Gamma genes regulate formation of fetal hemoglobin, which is switched to beta genes postnatally. It is about the 9th gestational week that the transcription switch from g chain to b chain production starts. Normally fetal hemoglobin synthesis declines gradually during this time but continues until 9 months of age. It is at about the 9th month after birth that the switch is completed.(Sarnaik 2005). This beta gene therein controls beta chain production in adults.
In patients suffering from beta thalassaemia, there is a switch from a normal gamma-globin gene, in the fetus to an abnormal beta-globin gene, in the adult. (Blau 1994). ...
tations have been described so far) Beta-thalassaemia major is hence a result of transmission of the mutated form of beta-globin gene from both parents, to the offspring. This results in inheritance of both defected form of the gene and has severe clinical manifestations for the patient.
Clinical features and abnormalities
As has been described above, beta thalassemia major refers to a decreased production of beta globin chains which are required for formation of normal haemoglobin in the blood. This results in decreased levels of normal haemoglobin(A) in the body. Interestingly there are evidences of increased levels of fetal (F) and abnormal haemoglobin (A2). Recent studies established that this abnormal increase in other Hb forms was due to production of excess of alpha chains, some of which are consequently utilized to synthesize hemoglobins which do not require beta chains, such as hemoglobin F (a2 g2) or hemoglobin A2 (a2 d2) and hence the elevated levels of such hemoglobins! (Perrimond 2001). Clinically this is very relevant as it leads to excessively reduced RBC life, this is primarily due to precipitation of free alpha chains on the RBCs.
Other clinical features are is extremely severe hypochromic anemia as a result of ineffective erythropoesis. There is also significant decrease in hemoglobin content per cell and microcytosis. In order to compensate for this the body attempts to increase the red cellproduction. This results in increase marrow cavities and 'extramedullary erythropoeisis' in the liver and spleen. The consequences of such endeavours may result in hepatosplenomegaly, bone defects and much discomfort (pain) in patients. In children, there is high incidence of growth deficit, cardiac problems and jaundice (due to excessive break down of red