How Is Thalassemia Inherited?
People who are at risk for the condition may wonder how thalassemia is inherited. The disease is inherited when the mutated thalassemia gene is passed from parents to their child. Worldwide, approximately 100,000 babies are born with severe forms of inherited thalassemia each year. However, the disease occurs more frequently in people of Italian, Greek, Middle Eastern, Southern Asian, and African descent.
Thalassemia is a group of inherited blood diseases that affect a person's ability to produce hemoglobin in red blood cells. A person with thalassemia does not have enough hemoglobin or red blood cells to carry oxygen throughout the body, which can cause mild to severe anemia.
Approximately 100,000 babies worldwide are born with severe forms of thalassemia each year. However, the condition occurs more frequently in people of Italian, Greek, Middle Eastern, Southern Asian and African ancestry.
The two main types of thalassemia are alpha and beta. Both types are inherited in the same manner. Parents who carry the mutated thalassemia gene can pass it on to their child. A child who inherits one mutated gene is considered to be a carrier, which is sometimes called thalassemia trait. Most carriers lead completely normal, healthy lives.
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 sign 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.