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Causes
By Mayo Clinic staffThe cause of thalassemia is defects in the genes that make hemoglobin. The only way to get thalassemia is to inherit one or more defective hemoglobin genes from your parents.
Hemoglobin is a red, iron-rich protein found in red blood cells. Hemoglobin enables red blood cells to carry oxygen from your lungs to all parts of your body and to carry carbon dioxide from other parts of your body to your lungs so that it can be exhaled. Most blood cells, including red blood cells, are produced regularly in your bone marrow — a red, spongy material found within the cavities of many of your large bones.
Thalassemia disrupts the normal production of hemoglobin and leads to a low level of hemoglobin and a high rate of red blood cell destruction, causing anemia. When you're anemic, your blood doesn't have enough red blood cells to carry oxygen to your tissues — leaving you fatigued.
There are two major types of thalassemia: alpha and beta, named for the two protein chains that make up normal hemoglobin. The type of thalassemia you have depends on the type of defective gene you inherit.
Alpha-thalassemia
Four genes are involved in making the alpha hemoglobin chain. You get two from each of your parents. If one or more of the alpha hemoglobin genes are defective, you develop alpha-thalassemia.
The more defective genes you have, the more severe your alpha-thalassemia:
- One gene. If only one of your alpha hemoglobin genes is defective, you'll have no signs or symptoms of thalassemia. But, you're a carrier of the disease and can pass it on to your children.
- Two genes. If you have two defective alpha hemoglobin genes, thalassemia signs and symptoms are mild. This condition may be called alpha-thalassemia minor, or you may be told you have an alpha-thalassemia trait.
- Three genes. If three of your alpha hemoglobin genes are defective, your signs and symptoms will be moderate to severe. This condition is also called hemoglobin H disease.
- Four genes. When all four alpha hemoglobin genes are defective, the condition is called alpha-thalassemia major or hydrops fetalis. It usually causes a fetus to die before delivery or shortly after birth.
Beta-thalassemia
Two genes are involved in making the beta hemoglobin chain. You get one from each of your parents. If one or both of the beta hemoglobin genes are defective, you develop beta-thalassemia.
- One gene. If one of your beta hemoglobin genes is defective, you have mild signs and symptoms. This condition is called beta-thalassemia minor or referred to as a beta-thalassemia trait.
- Two genes. If both of your beta hemoglobin genes are defective, your signs and symptoms will be moderate to severe. This condition is called beta-thalassemia major or Cooley's anemia. Babies born with two defective beta hemoglobin genes usually are healthy at birth, but develop signs and symptoms within the first two years of life.
- What are thalassemias? National Heart Lung and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/Thalassemia/Thalassemia_All.html. Accessed Nov. 19, 2008.
- Cunningham MJ. Update on thalassemia: Clinical care and complications. Pediatric Clinics of North America. 2008;55:447.
- Benz EJ. Clinical manifestations of the thalassemias. http://www.uptodate.com/home/index.html. Accessed Nov. 10, 2008.
- Schrier SL. Pathophysiology of beta thalassemia. http://www.uptodate.com/home/index.html. Accessed Nov. 10, 2008.
- Embury SH. Prenatal testing for the hemoglobinopathies and thalassemias. http://www.uptodate.com/home/index.html. Accessed Nov. 10, 2008.
- Benz EJ. Treatment of beta thalassemia. http://www.uptodate.com/home/index.html. Accessed Nov. 10, 2008.
