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.