CausesBy Mayo Clinic staff
Thalassemia is caused by mutations in the DNA of cells that make hemoglobin — the substance in your red blood cells that carries oxygen throughout your body. The mutations associated with thalassemia are passed from parents to children.
The mutations that cause thalassemia disrupt the normal production of hemoglobin and cause low hemoglobin levels 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.
Types of thalassemia
The type of thalassemia you have depends on the number of gene mutations you inherit from your parents and which part of the hemoglobin molecule is affected by the mutations. The more mutated genes, the more severe your thalassemia. Hemoglobin molecules are made of alpha and beta parts that can be affected by mutations.
Four genes are involved in making the alpha hemoglobin chain. You get two from each of your parents. If you inherit:
- One mutated gene, 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 mutated genes, your thalassemia signs and symptoms will be mild. This condition may be called alpha-thalassemia minor, or you may be told you have an alpha-thalassemia trait.
- Three mutated genes, your signs and symptoms will be moderate to severe. This condition is also called hemoglobin H disease.
- Four mutated genes, the condition is called alpha-thalassemia major or hydrops fetalis. It usually causes a fetus to die before delivery or a newborn to die shortly after birth.
Two genes are involved in making the beta hemoglobin chain. You get one from each of your parents. If you inherit:
- One mutated gene, you'll have mild signs and symptoms. This condition is called beta-thalassemia minor or referred to as a beta-thalassemia trait.
- Two mutated genes, 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.
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- Mueller BU. Prenatal testing for the hemoglobinopathies and thalassemias. http://www.uptodate.com/home/index.html. Accessed Jan. 3, 2011.