What is it? Thalassaemia is a group of inherited disorders that affect the amount of haemoglobin a person produces. Haemoglobin refers to a family of compounds all made up of haem (an iron-containing complex), and various globins (protein chains that surround the haem complex). Haemoglobin (Hb) molecules are found in all red blood cells, and are the reason for their red colour. They bind oxygen in the lungs, carry it through the bloodstream, and release it to the body’s tissues. Different types of haemoglobin are classified according to the type of protein chains they contain.
Normal adult haemoglobins include:
- Haemoglobin A (makes up about 95% - 98% of adult Hb). HbA contains two alpha (α) protein chains and two beta (ß) chains.
- HbA2 (makes up about 2% - 3.5% of adult Hb), has two alpha (α) and two delta (δ) chains
- HbF (up to 2%). This is the primary haemoglobin produced by the fetus during gestation. Its production usually falls to a low level within a year after birth. HbF has two alpha (α) and two gamma (γ) chains.
Mutations in the genes coding for the globin chains can cause disorders in haemoglobin production. There are 4 genes that code for alpha globin chains and 2 genes that code for the beta globin chains.
Inherited disorders of haemoglobin production fall into two categories:
- Thalassaemia: decreased production of normal haemoglobins
- Haemoglobinopathy: production of an abnormal haemoglobin molecule
Thalassaemias are a group of disorders in which mutations in one or more of the alpha or beta globin genes cause a reduction in the amount of the HbA produced. This leads to a reduction in HbA, the relative increase in the amount of minor haemoglobins HbA2 and HbF, and perhaps detection of unusual haemoglobin types.
The thalassaemias are usually classified by the type of globin chain whose synthesis is reduced.
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