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What Causes Thalassemias?

Your body makes three types of blood cells: red blood cells, white blood cells, and platelets (PLATE-lets). Red blood cells contain hemoglobin, an iron-rich protein that carries oxygen from your lungs to all parts of your body. Hemoglobin also carries carbon dioxide (a waste gas) from your body to your lungs, where it's exhaled.

Hemoglobin has two kinds of protein chains: alpha globin and beta globin. If your body doesn't make enough of these protein chains or they're abnormal, red blood cells won't form correctly or carry enough oxygen. Your body won't work well if your red blood cells don't make enough healthy hemoglobin.

Genes control how the body makes hemoglobin protein chains. When these genes are missing or altered, thalassemias occur.

Thalassemias are inherited disorders—that is, they're passed from parents to children through genes. People who inherit faulty hemoglobin genes from one parent but normal genes from the other are called carriers. Carriers often have no signs of illness other than mild anemia. However, they can pass the faulty genes on to their children.

People who have moderate to severe forms of thalassemia have inherited faulty genes from both parents.

Alpha Thalassemias

You need four genes (two from each parent) to make enough alpha globin protein chains. If one or more of the genes is missing, you'll have alpha thalassemia trait or disease. This means that your body doesn't make enough alpha globin protein.

  • If you're only missing one gene, you're a "silent" carrier. This means you won't have any signs of illness.
  • If you're missing two genes, you have alpha thalassemia trait (also called alpha thalassemia minor). You may have mild anemia.
  • If you're missing three genes, you likely have hemoglobin H disease (which a blood test can detect). This form of thalassemia causes moderate to severe anemia.

Very rarely, a baby is missing all four genes. This condition is called alpha thalassemia major or hydrops fetalis. Babies who have hydrops fetalis usually die before or shortly after birth.

Example of an Inheritance Pattern for Alpha Thalassemia

The picture shows one example of how alpha thalassemia is inherited. A child inherits four alpha globin genes-two from each parent. In this example, the father is missing two alpha globin genes and the mother is missing one alpha globin gene. Each child has a 25 percent chance of inheriting two missing genes and two normal genes (thalassemia trait), three missing genes and one normal gene (hemoglobin H disease), four normal genes (no anemia), or one missing gene and three normal genes (silent carrier).

The picture shows one example of how alpha thalassemia is inherited. The alpha globin genes are located on chromosome 16. A child inherits four alpha globin genes (two from each parent). In this example, the father is missing two alpha globin genes and the mother is missing one alpha globin gene.

Each child has a 25 percent chance of inheriting two missing genes and two normal genes (thalassemia trait), three missing genes and one normal gene (hemoglobin H disease), four normal genes (no anemia), or one missing gene and three normal genes (silent carrier).

Beta Thalassemias

You need two genes (one from each parent) to make enough beta globin protein chains. If one or both of these genes are altered, you'll have beta thalassemia. This means that your body won’t make enough beta globin protein.

  • If you have one altered gene, you're a carrier. This condition is called beta thalassemia trait or beta thalassemia minor. It causes mild anemia.
  • If both genes are altered, you'll have beta thalassemia intermedia or beta thalassemia major (also called Cooley's anemia). The intermedia form of the disorder causes moderate anemia. The major form causes severe anemia.

Example of an Inheritance Pattern for Beta Thalassemia

The picture shows one example of how beta thalassemia is inherited. A child inherits two beta globin genes-one from each parent. In this example, each parent has one altered beta globin gene. Each child has a 25 percent chance of inheriting two normal genes (no anemia), a 50 percent chance of inheriting one altered gene and one normal gene (beta thalassemia trait), or a 25 percent chance of inheriting two altered genes (beta thalassemia major).

The picture shows one example of how beta thalassemia is inherited. The beta globin gene is located on chromosome 11. A child inherits two beta globin genes (one from each parent). In this example, each parent has one altered beta globin gene.

Each child has a 25 percent chance of inheriting two normal genes (no anemia), a 50 percent chance of inheriting one altered gene and one normal gene (beta thalassemia trait), or a 25 percent chance of inheriting two altered genes (beta thalassemia major).

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Thalassemias Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Thalassemias, visit www.clinicaltrials.gov.

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Visit Children and Clinical Studies to hear experts, parents, and children talk about their experiences with clinical research.

 
July 03, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.

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