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Thalassemia is a genetic blood disorder that affects the production of hemoglobin. Normal adult hemoglobin is made up of 4 protein chains. There are 2 alpha chains and 2 beta chains. There are various degrees of severity of thalassemia that corresponds to the genetic coding for these alpha and beta chains.
Alpha thalassemia is due to impaired production of alpha protein chains. There are 2 genes on chromosome 16 that code for making alpha protein chains, each individual carries 4 alpha genes (abbreviated aa/aa). The severity of the disorder depends on the combination of genes inherited that code for the production of the alpha protein.
aa/aa – normal coding for alpha protein production.
aa/a- (3 normal genes with one gene to code for alpha protein production is missing or is defective)
This has been called alpha thalassemia minima, silent carrier of alpha thalassemia, alpha thalassemia-2 trait, or heterozygosity for alpha ( ) thalassemia. These persons do not exhibit any symptoms. Most of these persons are diagnosed only with specialized DNA blood tests.
aa/– or a-/a- (two normal genes with two genes that code for alpha protein production are missing or defective)
This is called alpha thalassemia minor or alpha thalassemia-1 trait. Persons with this genetic coding may have minimal anemia and slight abnormalities on their complete blood count (CBC) such as small red blood cells that have a more pale color.
a-/– (one normal gene with three genes that code for alpha protein production are missing or defective)
This is called hemoglobin H (HbH) disease. Because there is so little alpha protein made, the beta proteins are in excess. These excess beta chains group together in fours to make hemoglobin H. Unfortunately, hemoglobin H is not good at transporting oxygen. The Hemoglobin H is insoluable and causes the membrane of the red blood cell to break open. This results in a hemolytic anemia (low blood counts because the red blood cells break open and are destroyed). Persons with HbH disease have medical problems similar to other hemolytic anemias. They can develop large spleens that often require splenectomy. They can develop leg ulcers. Most patients do not require transfusion support until after the first decade of life. However, into their 20’s and 30’s most patients often require transfusion support and/or splenectomy. As in other disorders that require frequent blood transfusions, iron overload can become an issue and is treated accordingly with iron chelating agents.
There are varying degrees of Hemoglobin H disease, including Hemoglobin H – constant spring, that can be further discussed with your health care provider.
–/– (no normal genes are present, all four genes that code for alpha protein production are either missing or defective)
This is called alpha thalassemia major, or hemoglobin Bart’s, no alpha protein is produced. This genetic combination almost always results in fetal death during the late second to mid-third trimester. Very rare live births have been reported, however this condition leads to hydrops fetalis and these infants usually die within a few hours after birth. Mothers that carry these children are at risk for severe pregnancy and delivery complications.
Beta thalassemia is due to impaired production of beta protein chains. Each individual carries 2 beta genes. The severity of the disorder depends on the combination of genes inherited that code for the production of the beta protein.
There are more than 30 different genetic mutations that code for a decreased amount of beta protein to be made. There are more than 40 different genetic mutations that code for no beta protein to be made. As a result, this disease is highly variable in terms of symptoms and severity.
Beta thalassemia minor
This is also called beta thalassemia trait. Individuals have inherited one gene that codes for decreased or absent beta protein production. The other gene inherited is a normal gene. These patients usually do not have any symptoms, but are usually found to be mildly anemic on blood counts.
Beta thalassemia intermedia
This term applies to patients with disease of intermediate severity. Genetically, they have usually inherited genes from both parents that code for decreased production of beta protein production. They are anemic, but usually only require transfusions during episodes of acute illness, such as an infection, which can slow normal manufacturing of blood cells.
Beta thalassemia major (Cooley’s Anemia)
These patients have inherited genes from both parents that codes for no beta protein to be made. They are unable to make any normal adult hemoglobin. These patients have profound anemia. They are dependent on blood transfusions starting in the first year of life. Due to the need for life long blood transfusions, excess iron accumulates in the body. These patients need special medication called iron chelators (Exjade, Desferal) to remove the excess iron from their blood and tissues.
Inheritance of Thalassemia
When each parent carries a gene that codes for decreased or no alpha or beta protein to be made, with each pregnancy, there is a chance that each parent will pass the thalassemia gene onto their children. This inheritance happens purely by chance – there is nothing parents do, or do not do, that will cause their child to inherit the gene for thalassemia. Genetic counseling is available at our center for couples who carry thalassemia.