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Written by madmax
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Monday, 01 March 2010 00:14 |
Thalassemia, inherited blood disease resulting from defective production of hemoglobin, the protein that transports oxygen in the blood. People with thalassemia typically develop anemia, a condition that results in inadequate delivery of oxygen to the body’s tissues, which can produce symptoms ranging from fatigue to organ damage. Two main types of thalassemia exist, alpha thalassemia and beta thalassemia.
While the severity of these two thalassemia types varies, in general, alpha thalassemia is less severe. Patients living with this form of the disease usually have mild to moderate symptoms, which are often manageable without treatment. Beta thalassemia, on the other hand, is generally much more severe. Untreated, it is usually fatal in the first few years of life.
More common worldwide than beta thalassemia, alpha thalassemia occurs throughout Southeast Asia and China and sometimes among people of Mediterranean descent. Beta thalassemia primarily affects people of Mediterranean or Middle Eastern descent. Approximately 100,000 babies are born with thalassemia worldwide each year, according to the March of Dimes, an organization devoted to the prevention of birth
Produced in red blood cells, hemoglobin is a protein made up of four chains of amino acids: two identical alpha chains and two identical beta chains. Thalassemia is caused by an imbalance in the production of alpha and beta chains, an imbalance that is caused by a mutation, or change, in the genes that direct their production. A mutation to the alpha genes decreases the production of alpha chains, resulting in alpha thalassemia. A mutation to the beta genes decreases the production of beta chains, resulting in beta thalassemia.
Many different mutations cause thalassemia, but all the mutations can be divided into two main groups. Some mutations affect the structure of alpha or beta chains, while others affect the rate at which the chains are produced. The severity of disease in any thalassemia patient depends on the degree of imbalance between alpha and beta chain production. In general, mutations that affect the structure of the chains result in more severe disease than mutations that affect the rate at which the chains are produced.
Thalassemia is an autosomal recessive genetic disorder. Each person has two copies of the beta gene, one inherited from each parent. Beta thalassemia results when both copies of the beta gene are abnormal. A person with only one abnormal copy of the beta gene does not develop the disease but is a carrier of beta thalassemia. When two carriers of beta thalassemia have children, each child has a 25 percent chance of inheriting two abnormal copies of the beta gene and, therefore, developing the disease. Each child has a 50 percent chance of inheriting one abnormal gene and being a carrier, and a 25 percent chance of inheriting two normal beta genes.
The inheritance of alpha thalassemia is more complicated because each person normally has four copies of the alpha gene, two inherited from each parent. People with one or two abnormal alpha genes are carriers and do not develop the disease. Children who inherit three abnormal alpha genes have a form of alpha thalassemia that makes them anemic but typically does not shorten their life span. Those who inherit four abnormal alpha genes have a severe form of alpha thalassemia that results in death in the womb or within the first few hours of life.
Carriers of thalassemia typically do not have symptoms of thalassemia and do not require treatment. In fact, carriers of thalassemia are partially resistant to malaria, a serious and often fatal parasitic disease that is prevalent in tropical and subtropical regions of the world. In some areas where malaria is common, up to 20 percent of people are thalassemia carriers. Scientists believe that the thalassemia genes have become widespread in these areas because of the advantage these genes confer on carriers.
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Mad Max
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