Thalassemia is caused by gene changes in cells that make hemoglobin. Hemoglobin is the protein in red blood cells that carries oxygen throughout the body. The gene changes linked with thalassemia are passed from parents to children.
Hemoglobin molecules are made of protein chains called alpha and beta chains. These chains are affected by gene changes. With thalassemia, the body doesn't make enough of either the alpha or the beta chains. That causes you to get either alpha-thalassemia or beta-thalassemia, the two main types of the condition.
In beta-thalassemia, the gene change is an alteration in the DNA. Other terms used to describe these changes include mutation or variation. In alpha-thalassemia, the altered DNA consists of missing one or more copies of the four genes that program the alpha chain. This also is termed "deletion."
With alpha-thalassemia, the seriousness of the condition depends on the number of missing genes you inherit from your parents. The more missing copies of the genes, the worse your thalassemia.
With beta-thalassemia, the seriousness of the condition depends on which part of the hemoglobin molecule is affected.
Alpha-thalassemia
Four genes are involved in making the alpha hemoglobin chain. You get two from each of your parents. The seriousness of alpha-thalassemia depends on how many copies of the genes are missing:
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If one copy of the gene is missing, you'll have no symptoms of thalassemia. But you carry the disease and can pass it on to your children.
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If two copies of the genes are missing, your thalassemia symptoms likely will be mild. You might hear this condition called alpha-thalassemia trait.
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If three copies of the genes are missing, your symptoms likely will be moderate to severe.
It's rare to be missing all four copies of the genes. It usually leads to stillbirth. That's the loss of a pregnancy at or after 20 weeks. Babies born with four missing genes often die shortly after birth. Or they need blood transfusions for the rest of their lives. Sometimes, a child born with this condition can be treated with blood transfusions and a stem cell transplant.
Beta-thalassemia
Two genes are involved in making the beta hemoglobin chain. You get one from each of your parents. Unlike the missing genes that cause alpha-thalassemia, small changes in the gene cause beta-thalassemia. These changes lead to reduced production of the beta chain. If you inherit:
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One gene with changes, you'll usually have mild symptoms. This condition is called nontransfusion-dependent thalassemia. If you have no symptoms, you may hear your condition called beta-thalassemia trait or thalassemia minor.
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Two genes with changes, your symptoms typically will be moderate to severe. This condition is called transfusion-dependent beta-thalassemia or thalassemia major.
Babies born with two changed beta hemoglobin genes usually are healthy at birth. They often get symptoms within the first two years of life. But it is possible to get a milder form of the disease with two changed genes.