There are two main types: alpha and beta. Beta thalassemia is the most common.
You need both alpha- and beta-globin to make hemoglobin. Beta thalassemia occurs when one or both of the two genes that make beta-globin don't work or only partly work as they should.
If you have one damaged gene, you may have mild anemia and probably won't need treatment. This is called beta thalassemia minor or beta thalassemia trait. It happens when you get a normal gene from one parent and a thalassemia gene from the other.
When both genes are damaged, it means you got a thalassemia gene from each parent. You may have moderate or severe anemia.
If you have moderate anemia (beta thalassemia intermedia), you may need blood transfusions.
People with severe anemia (called beta thalassemia major or Cooley's anemia) need blood transfusions throughout life. Symptoms of anemia usually begin within a few months after birth.
This type occurs when one or more of the four alpha-globin genes that make hemoglobin are missing or damaged.
If one gene is missing or damaged: Your red blood cells might be smaller than normal. You will have no symptoms and you will not need treatment. But you are a silent carrier. This means you don't have the disease but can pass the defective gene to your child.
If two genes are missing or damaged: You will have very mild anemia that will typically not need treatment. This is called alpha thalassemia minor or alpha thalassemia trait.
If three genes are missing: You will have mild to moderately severe anemia. This is sometimes called hemoglobin H disease. If it is severe, you may need blood transfusions.
If all four genes are missing: This is called alpha thalassemia major or hydrops fetalis. The fetus will be stillborn, or the child will die soon after birth.