Pathophysiology
Normally, hemoglobin is composed of four protein chains, two α and two β globin chains arranged into a heterotetramer. In thalassemia, patients have defects in either the α or β globin chain (unlike sickle-cell disease, which produces a specific mutant form of β globin), causing production of abnormal red blood cells.
The thalassemias are classified according to which chain of the hemoglobin molecule is affected. In α thalassemias, production of the α globin chain is affected, while in β thalassemia production of the β globin chain is affected.
The β globin chains are encoded by a single gene on chromosome 11; α globin chains are encoded by two closely linked genes on chromosome 16. Thus, in a normal person with two copies of each chromosome, there are two loci encoding the β chain, and four loci encoding the α chain. Deletion of one of the α loci has a high prevalence in people of African or Asian descent, making them more likely to develop α thalassemias. β Thalassemias are not only common in Africans, but also in Greeks and Italians.
Read more about this topic: Thalassemia