What is alpha thalassemia?
Thalassemia is an inherited disorder that affects the production of normal hemoglobin (a type of protein in red blood cells that carries oxygen to the tissues of the body). Thalassemia includes a number of different forms of anemia. The severity and type of anemia depend on the number of genes that are affected.
What causes alpha thalassemia?
Alpha thalassemia is caused by mutations in the alpha chain of the hemoglobin molecule. Normally, there are two alpha chain genes located on each #16 chromosome, for a total of 4. The alpha chain is an important component of fetal hemoglobin (which is usually made before birth) and hemoglobin A and hemoglobin A2 (which are present after birth). How these genes are altered determines the specific type of alpha thalassemia in a child:
Alpha thalassemia major (also called Hb Bart syndrome). With this disorder, all four alpha chain genes are deleted. Alpha thalassemia major develops before birth and results in hydrops fetalis, a condition in which the body has excess fluid. The fetus can also have other problems including severe anemia, enlargement of the liver and spleen (hepatosplenomegaly), and defects in the heart, urinary system, or genitals. Most babies with hydrops fetalis due to alpha thalassemia major die during pregnancy or soon after birth. The mother can have pregnancy complications including preeclampsia (high blood pressure), bleeding problems, and preterm delivery.
Hemoglobin H disease. Three alpha chain genes are deleted. Hemoglobin H disease occurs when a person has only one functioning alpha chain gene, resulting in a hemolytic anemia that can worsen with febrile illness or exposure to certain drugs, chemicals, or infectious agents. People with hemoglobin H disease are at increased risk to have a child with alpha thalassemia major, since they carry one #16 chromosome with an alpha chain two gene deletion (cis deletion).
Alpha thalassemia carrier. Two alpha chain genes are deleted, either:
Both from the same #16 chromosome, called a cis deletion
One from each #16 chromosomes, called a trans deletion
When both parents are carriers of the cis deletion, there is a one in four, or 25 percent, chance with each pregnancy, to have a baby with alpha thalassemia major. A common hemoglobin test, hemoglobin electrophoresis, cannot diagnose alpha thalassemia. Carriers of the cis deletion versus the trans deletion can be distinguished by DNA analysis only. DNA testing is usually done from a blood sample to look at the alpha chain genes on each #16 chromosome to determine which genes are deleted.
How is alpha thalassemia diagnosed?
Alpha thalassemia is most commonly found in Africa, the Middle East, India, Southeast Asia, southern China, and the Mediterranean region. Carrier status can be determined by the following:
Complete blood count (CBC). A measurement of size, number, and maturity of different blood cells in a specific volume of blood.
Hemoglobin electrophoresis with A2 and F quantitation. A lab procedure that differentiates the types of hemoglobin present. This test can diagnose beta thalassemia and other hemoglobin changes, but not alpha thalassemia.
Iron studies, FEP (free-erythrocyte protoporphyrin) and ferritin. These studies are done to exclude iron deficiency anemia.
All of these studies can be performed from a single blood sample. Prenatal diagnosis is determined from CVS (chorionic villus sampling) or amniocentesis.
Treatment for alpha thalassemia
Specific treatment for alpha thalassemia will be determined by your child's doctor based on:
Your child's age, overall health, and medical history
Extent of the disease
Your child's tolerance for specific medications, procedures, or therapies
Expectations for the course of the disease
Your opinion or preference
Treatment for alpha thalassemia may include:
Daily doses of folic acid
Blood transfusions (as needed) and iron chelation (removal of iron) therapy due to iron overload
Surgical removal of the spleen (if necessary)
Allogeneic stem cell transplantation