Causes of Thalassemia
Four genes are involved in making the alpha-globin part of hemoglobin -- two from each parent. Alpha thalassemia occurs when one or more of these genes are variant or missing. Examples of alpha thalassemia include:
- People with only one gene affected are called "silent carriers" and have no signs of illness.
- People with two genes affected (alpha thalassemia trait or alpha thalassemia minor) have mild anemia and are considered carriers.
- People with three genes affected (hemoglobin H disease) have moderate to severe anemia.
- Until recently, babies with all four genes affected (alpha thalassemia major or hydrops fetalis) could not survive and usually died before birth. Today, many of these babies can survive with treatment.
If two people with alpha thalassemia trait (carriers) have a child, the baby could have a mild or severe form of alpha thalassemia or the baby could be healthy.
Two genes are involved in making the beta-globin part of hemoglobin -- one from each parent. Beta thalassemia occurs when one or both of the two genes are variant. Examples include:
- If one gene is affected, a person is a carrier and has mild anemia. This condition is called beta thalassemia trait or beta thalassemia minor.
- If both genes are variant, a person may have moderate anemia (beta thalassemia intermedia or mild Cooley's anemia) or severe anemia (beta thalassemia major or Cooley's anemia).
If two people with beta thalassemia trait (carriers) have a baby, one of three things can happen:
- The baby could receive two normal genes (one from each parent) and have normal blood (1 in 4 chance)
- The baby could receive one normal gene from one parent and one variant gene from the other parent, and have thalassemia trait (2 in 4 chance)
- The baby could receive two thalassemia genes (one from each parent) and have a moderate to severe form of the disease (1 in 4 chance).