An inherited type of anaemia affecting production of haemoglobin, the oxygen-carrying pigment in red blood cells
In thalassaemia, an inherited genetic defect prevents the normal formation of haemoglobin, the oxygen-carrying pigment inside red blood cells. Red cells containing the defective haemoglobin carry less oxygen than normal and are destroyed prematurely, reducing oxygen transport to the body tissues.
The body tries to compensate by producing additional red blood cells throughout the bone marrow and in the liver and spleen, where red blood cells are not normally formed. The marrow expands due to overactivity, which may lead to thickening of the bones of the skull and face. The liver and spleen may become enlarged as they produce and, in the case of the spleen, destroy large numbers of the abnormal red blood cells. Thalassaemia mainly affects people from Mediterranean countries, the Middle East, Southeast Asia, and Africa.
A normal haemoglobin molecule contains four protein (globin) chains: two alpha and two beta chains. Different genes are responsible for the production of each type of chain. Thalassaemia is caused by one or more genetic defects and results in a failure to produce sufficient quantities of either the alpha or the beta globin chains.
Thalassaemia due to abnormal beta chains is more common. A person inherits two copies of the gene for haemoglobin beta chains, one copy from each parent. If one of those genes is defective, the individual will typically have no symptoms and is termed a carrier. If both genes are defective, the individual will have symptoms of thalassaemia.
Thalassaemia due to abnormal alpha chains is comparatively rare in the UK. A person inherits four copies of the genes for haemoglobin alpha chains, two from each parent. If one or two of those genes are defective, the individual will typically be a carrier with no symptoms, although occasionally there may be mild anaemia. If three genes are defective, the individual will usually have symptoms, such as anaemia. If all four genes are defective, the fetus will die before birth unless blood transfusions are given while the fetus is still in the uterus and continued after birth. However, such treatment is not always successful.
Genetic testing is available for women or couples planning to have children and, if a defective gene is identified, they may want to consider genetic counselling. In addition, tests for thalassaemia are routinely offered to all pregnant women in England (and can be requested in other parts of the UK). If testing indicates the fetus has thalassaemia, counselling will be offered to discuss whether the woman wants to continue the pregnancy. In England, newborn babies are also routinely given a screening test for thalassaemia. In other parts of the UK, the newborn thalassaemia test is available on request.
Carriers of beta-thalassaemia do not usually have symptoms. However, if an individual inherits two defective genes for beta-thalassaemia, symptoms of severe anaemia usually appear between 4 and 6 months of age. These symptoms may include:
Shortness of breath on mild exertion.
Swelling of the abdomen due to an enlarged liver and spleen.
Affected children have slow growth, and sexual development is delayed. The bones of the skull and face may thicken as the bone marrow expands.
Carriers of alpha-thalassaemia (with one or two defective genes) often have no symptoms, although some individuals with two defective genes may have mild anaemia. For those with three defective genes, the symptoms are similar to those of beta-thalassaemia, although they may not appear until later in childhood or early adulthood.
If the thalassaemia is mild, treatment may not be needed, although folic acid supplements (see Vitamins) may be recommended to help stimulate the production of red blood cells. If the condition is severe, regular blood transfusions may be needed for life. However, frequent blood transfusions can lead to a build-up of iron in the heart, liver, and pancreas, causing progressive damage to these organs. To counteract this build-up, treatment with desferrioxamine, desferasirox, or deferiprone (drugs that allow the kidneys to excrete more iron than usual) may be needed. If the spleen is enlarged, it may need to be removed. In severe cases, a stem cell transplant may be considered.
People with mild thalassaemia have a normal life span. Some people who have severe thalassaemia die early in childhood, but life expectancy can be greatly improved with regular transfusions.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.