The most common 'single gene defect' in man comprises primarily of the inherited hemoglobin disorders. These hemoglobinopathies (blood or hemoglobin disorders) together, also have the highest incidence of prevalence worldwide in terms of incidence of single gene disorders.
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). ...