Alpha Thalassemia

What is Alpha Thalassemia?

Alpha Thalassemia meaning Alpha thalassemia is caused by mutations in the alpha chain of the hemoglobin molecule. Normally, there are two genes coding for the alpha chain on each #16 chromosome, for a total of four genes. The alpha chain is an important component of fetal hemoglobin (usually made before birth) and hemoglobin A and hemoglobin A2 (present after birth). How these genes are altered determines the specific type of alpha thalassemia in a person: Alpha thalassemia major. All four alpha chain genes are deleted. Hemoglobin Bart hydrops fetalis is another term for this condition. This results in an anemia that is so severe that death usually occurs in utero (prior to birth). Alpha thalassemia carrier. Two alpha chain genes are deleted. Alpha thalassemia minor or alpha thalassemia-1 trait are other terms for this condition. If both deleted genes are from the same #16 chromosome, it is called a cis deletion and is inherited from one parent. If instead one gene is missing from both #16 chromosomes, it is called a trans deletion and is inherited from both parents. This results in an anemia that is usually mild to moderate, but can be severe. 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. Identifying whether an alpha thalassemia carrier has the cis deletion versus two trans deletions requires testing by DNA (deoxyribonucleic acid) analysis. DNA testing is usually done from a blood sample, and looks at the alpha chain genes on each #16 chromosome, to determine which are deleted. Hemoglobin H disease. Three alpha chain genes are deleted. Hemoglobin H disease occurs when a person inherits a cis deletion from one parent and a trans deletion from the other so that they have only one functioning alpha chain gene. This results in a severe hemolytic anemia that can worsen with febrile illness or exposure to certain drugs, chemicals, or infectious agents, and often requires blood transfusions. The effects on the body of hemoglobin H disease are more serious than those of the thalassemia trait. 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). Silent alpha thalassemia carrier. One alpha chain gene is deleted (the other three are normal). Alpha thalassemia minima or alpha thalassemia-2 trait are other terms for this condition. Blood tests are usually normal, though the red cells may be small, leading to a suspicion that the patient is a silent carrier. The only way to confirm a silent carrier is by DNA studies.

 

reference: national Cancer Institute – Glossary for Registrars

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