Alpha-thalassemia

Overview

What is alpha-thalassemia?

Alpha-thalassemia is a fairly common blood disorder that results in reduced amounts of hemoglobin, the protein in red blood cells that carries oxygen to cell in the body. This lowers the amount of oxygen that cells receive, causing various health problems, including anemia.

There are two types of alpha-thalassemia that can cause serious health problems and two types that can cause mild symptoms. The most serious is called hemoglobin Bart. Fetuses affected with hemoglobin Bart usually do not survive beyond the newborn period. While still in the uterus, they experience health complications, including swelling, fluid buildup around the organs, heart defects and genital abnormalities. The mothers of these fetuses experience health complications including preeclampsia, (extreme hypertension), excessive amniotic fluid or reduced amniotic fluid, bleeding in the genital tract, and premature delivery. Due to the lack of very effective treatment and severe complications, termination of these pregnancies is sometimes considered. The less severe form of alpha-thalassemia is called hemoglobin H. Symptoms associated with this form include enlarged spleen, anemia, yellowing of the eyes and skin, and bone overgrowth. Symptoms vary from mild to severe. These individuals typically live into adulthood.

Alpha-thalassemia is caused by deletions or mutations in the HBA1 and/or HBA2 genes, meaning pieces of the gene are missing or changed. Both of these genes tell the body to make a protein called alpha globin, which is a component of hemoglobin. Hemoglobin is the protein in red blood cells responsible for carrying and delivering oxygen to cells throughout the body. We each have two copies, called alleles, of HBA1 and HBA2, for a total of four alleles. When one or more of these alleles has a change, the body cannot produce alpha globin correctly, resulting in a reduced ability of red blood cells to carry oxygen throughout the body. If three or four alleles are changed, the cells produce an abnormal form of hemoglobin called hemoglobin H or hemoglobin Bart, respectively. These types of hemoglobin do not easily release oxygen to the cells. Therefore, cells can not get the oxygen they need. Hemoglobin H can also form abnormal clumps in the cells that can lead to cell death. People with two alleles changed have hemoglobin trait and may have anemia. People with only one allele changed are called silent carriers.

Because two genes are involved, the inheritance of alpha-thalassemia is complex, but usually follows an autosomal recessive pattern of inheritance. Autosomal recessive inheritance means that peope who have one changed allele do not have disease (and are called carriers) while, those with two changed alleles have disease. Alpha-thalassemia is more complicated because there are two genes involved. An individual can inherit between 0 and 4 changed copies of genes HBA1 and/or HBA2. In general, people with more changed copies have more health complications as compared to individuals with fewer changed gene copies.

Alpha-thalassemia can be diagnosed by blood analysis. Genetic testing can also be performed to determine the exact changes to the genes involved, HBA1 and HBA2. Blood testing involves analysis of the size, shape, color and number of red blood cells. The hemoglobin is also analyzed to determine how much and which types of hemoglobin are present. Genetic testing can determine the specific changes of the genes involved, HBA1 and HBA2. Understanding the exact changes involved with these genes will enable more accurate prediction of the severity of the disease and also allow the health care provider to provide an accurate risk of future pregnancies being affected. Genetic testing is necessary if parents are concerned their pregnancy is affected and want to test their fetus before delivery.

Treatment for alpha-thalassemia depends on the specific type an individual has. Fetuses with hemoglobin Bart typically do not survive beyond the newborn period. They usually have serious symptoms including birth defects of the heart, limbs and genitals, and delays in development. The mothers of these infants often experience maternal complications including severe anemia, preeclampsia, an abnormal amount of amniotic fluid, and delivery complications. Individuals with hemoglobin H disease benefit from folic acid supplements, and a non-iron containing multivitamin may be recommended. Patients should avoid oxidative compounds and medications, and a high iron diet. Any infections should be treated promptly. There should be ongoing monitoring of growth, bone health, spleen size, inflammation of the gallbladder, leg ulcers and fatigue. Blood transfusions, or removal of the spleen or gallbladder may be indicated. During pregnancy, women with Hemoglobin H disease should be monitored for potential serious complications. People who are carriers of alpha-thalassemia may have mild anemia, which would need monitoring and potentially treatment.

SOURCE: Emory University - Department of Human Genetics in collaboration with ThinkGenetic • https://www.thinkgenetic.com/diseases/alpha-thalassemia-8207/overview/5562 • DATE UPDATED: 2016-06-12

References

Alpha thalassemia. (2009). Genetics Home Reference. https://ghr.nlm.nih.gov/condition/alpha-thalassemia

Origa, R., Moi, P., Galanello, R., & Cao, A. (2013). Alpha-Thalassemia. GeneReviews at GeneTests Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2013. Available at http://www.genetests.org. Accessed (2/29/2016).

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