Thalassemia is an inherited blood disorder that affects the production of normal hemoglobin (a type of protein in red blood cells that carries oxygen to the tissues in the body). Thalassemia includes a number of different forms of anemia. The severity and type of anemia depends upon the number of genes that are affected.
Two types of thalassemia in children are alpha thalassemia and beta thalassemia; severe beta thalassemia is also known as Cooley's anemia.
Alpha Thalassemia in Children
What causes alpha thalassemia?
Alpha thalassemia is caused by mutations in the alpha chain of the hemoglobin molecule. Normally, there are a total of four alpha chains. 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 missing. 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 moderate to severe anemia that can worsen with illness or exposure to certain drugs, chemicals, or infections. People with hemoglobin H disease are at increased risk to have a child with alpha thalassemia major.
- Silent alpha thalassemia carrier. One alpha chain gene is deleted (the other three are normal). Blood tests are usually normal, and the only way to confirm a silent carrier is by DNA studies.
- Alpha thalassemia carrier. Two alpha chain genes are deleted, either:
- Both from the same chromosome, called a cis deletion
- One from each chromosome, called a trans deletion
This carrier state is not associated with any medical problems, but very mild anemia is often present on laboratory testing.
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.
Alpha thalassemia diagnosis and treatment
Beta Thalassemia (Cooley's Anemia) in Children
What is beta thalassemia?
Beta thalassemia is caused by mutations in the beta chain of the hemoglobin molecule. Normally there are two beta chains. How these genes are altered determines the specific type of beta thalassemia in a child:
- Beta thalassemia major (Cooley's anemia). Both (two) beta chain genes have deletions, causing the most severe type of beta thalassemia. Thalassemia major patients need frequent blood transfusions and may not survive a normal lifespan. During the first 1 to 2 years of life, they can be pale, fussy, have a poor appetite, and have many infections. Without treatment, the spleen, liver, and heart become enlarged, and bones can become thin, brittle, and deformed. A major problem is the buildup of iron in the heart and other organs, resulting in heart failure for some patients in their teens or early twenties.
- Thalassemia minor or thalassemia trait. One beta gene has a deletion, resulting in anemia. Thalassemia minor is further divided into thalassemia minima (a person has little to no symptoms) and thalassemia intermedia (a person has moderate to severe anemia).
People with thalassemia minor have a 50/50 chance to pass the gene to their offspring, who would also have thalassemia minor. Many people are given iron replacement under the mistaken belief that their anemia is the iron-deficient type. Since too much iron can be harmful, it is important to demonstrate conclusively that a patient has iron deficiency before beginning treatment. If there is any question as to whether a patient has thalassemia, it is wise to consult a hematologist before beginning any treatment.
Thalassemia major occurs when an abnormal gene is inherited from each of two carrier parents who have thalassemia minor.
Beta thalassemia diagnosis and treatment