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Alpha-thalassemia is a blood disorder that reduces the body's production of hemoglobin. Affected people have anemia, which can cause pale skin, weakness, fatigue, and more serious complications. Two types of alpha-thalassemia can cause health problems: the more severe type is known as Hb Bart syndrome; the milder form is called HbH disease. Hb Bart syndrome may be characterized by hydrops fetalis; severe anemia; hepatosplenomegaly; heart defects; and abnormalities of the urinary system or genitalia. Most babies with this condition are stillborn or die soon after birth. HbH disease may cause mild to moderate anemia; hepatosplenomegaly; jaundice; or bone changes. Alpha-thalassemia typically results from deletions involving the HBA1 and HBA2 genes. The inheritance is complex, and can be read about here. No treatment is effective for Hb Bart syndrome. For HbH disease, occasional red blood cell transfusions may be needed.
Source: GARD Last updated on 05-01-20
The inheritance of alpha-thalassemia is complex because the condition involves two genes: HBA1 and HBA2. People have two copies of the HBA1 gene and two copies of the HBA2 gene in each cell. Each copy is called an allele. Therefore, there are 4 alleles that produce alpha-globin, the protein that results from these genes. For each of the 2 genes, one allele is inherited from a person's father, and the other is inherited from a person's mother - so each person inherits 2 alleles from each parent. The different types of alpha- thalassemia result from the loss of some or all of these alleles.
If both parents are missing at least one alpha-globin allele, each of their children are at risk of having Hb Bart syndrome or hydrops fetalis, hemoglobin H (HbH) disease, or alpha-thalassemia trait. The precise risk depends on how many alleles are missing and which combination of the HBA1 and HBA2 genes is affected.
In most cases:
When there are 4 mutated alleles, the condition is called alpha-thalassemia major or hydrops fetalis. In these cases, an affected fetus usually does not survive to birth, or an affected newborn does not survive long after birth.
Last updated on 05-01-20
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