n WHO GETS THALASSEMIA? Most people who have thalassemia are descendants from Africa, Southeast Asia, Southern China, India, Pakistan, the Middle East, Greece, and Italy. More than 2 million Americans carry the thalassemia trait. About 1,000 people are affected by beta thalassemia major, the most severe type of thalassemia.
n WHAT ARE THE TYPES OF THALASSEMIA? There are two main types of thalassemia: alpha thalassemia and beta thalassemia. People who did not inherit four normal alpha globin genes have alpha thalassemia . People who did not inherit two normal beta globin genes have beta thalassemia . Each of these types of thalassemia has different subtypes.
Alpha Thalassemia Subtypes
SILENT CARRIER One of the four alpha globin genes is missing or abnormal. This type of thal- assemia usually does not cause any health problems, and there is no anemia. Patients should be aware that they are carriers of alpha thalassemia because they risk passing it onto their children. Alpha thalassemia may show up on routine blood work or as part of newborn screening. ALPHA THALASSEMIA TRAIT/MILD ALPHA THALASSEMIA Two of the four alpha globin genes are missing or abnormal. This type of thalassemia causes smaller red blood cells and mild anemia.
There may be one abnormal gene on each side of chromosome 16, or both of the abnormal genes can be on the same half of chromosome 16. This is called a cis mutation and is more common in people of Asian descent.
HEMOGLOBIN H DISEASE Three of the four alpha globin genes are missing or abnormal. One of the strands of chromosome 16 will have two abnormal genes, or the cis mutation. The other half will have one normal gene and one abnormal gene. Hemoglobin H disease will cause moderate to severe anemia. There can be serious health problems, such as an enlarged spleen, bone deformities, and fatigue. Because the cis mutation is more common in people of Asian descent, Hemoglobin H also is more common in this group. HYDROPS FETALIS/ALPHA THALASSEMIA MAJOR All four alpha globin genes are missing or defective. Most babies with this type of thalassemia will die shortly before or after birth. If parents are known to carry a cis mutation, testing for hydrops fetalis/alpha thalassemia major may be done before birth. In this case, blood transfusions can be given to the fetus during pregnancy. After birth, the child will then require lifelong blood transfusions and ongoing medical care.
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