Diseases

Hemoglobin H Disease (Alpha Thalassemia) Information

Alpha Thalassemia Facts*

*Alpha thalassemia facts medical author: Melissa Conrad Stoppler, MD

• Alpha thalassemia is a blood disorder that reduces the production of normal hemoglobin, the protein in red blood cells that carries oxygen to cells throughout the body.
• There are four types of alpha thalassemia, hemoglobin Bart hydrops fetalis syndrome or Hb Bart syndrome (the more severe form), HbH disease, silent carrier state and trait.
• Alpha thalassemia occurs frequently in people from Mediterranean countries, North Africa, the Middle East, India, and Central Asia.
• Alpha thalassemia typically results from deletions involving the HBA1 and HBA2 genes.
• People who have alpha thalassemia trait can have mild anemia. However, many people with this type of thalassemia have no signs or symptoms.
• Treatments for thalassemias depend on the type and severity of the disorder.

What Genes Are Related to Alpha Thalassemia

Alpha thalassemia typically results from deletions involving the HBA1 and HBA2 genes. Both of these genes provide instructions for making a protein called alpha-globin, which is a component (subunit) of hemoglobin. People have two copies of the HBA1 gene and two copies of the HBA2 gene in each cell. Each copy is called an allele. For each gene, one allele is inherited from the father, and the other is inherited from the mother. As a result, there are four alleles that produce alpha-globin. The different types of alpha thalassemia result from the loss of some or all of these alleles. Hb Bart syndrome, the most severe form of alpha thalassemia, results from the loss of all four alpha-globin alleles. HbH disease is caused by a loss of three of the four alpha-globin alleles. In these two conditions, a shortage of alpha-globin prevents cells from making normal hemoglobin. Instead, cells produce abnormal forms of hemoglobin called hemoglobin Bart (Hb Bart) or hemoglobin H (HbH). These abnormal hemoglobin molecules cannot effectively carry oxygen to the body's tissues. The substitution of Hb Bart or HbH for normal hemoglobin causes anemia and the other serious health problems associated with alpha thalassemia. Two additional variants of alpha thalassemia are related to a reduced amount of alpha-globin. However, cells still produce some normal hemoglobin, these variants tend to cause few or no health problems, and the loss of two of the four alpha-globin alleles results in alpha thalassemia trait. People with alpha thalassemia trait may have unusually small, pale red blood cells and mild anemia. A loss of one alpha-globin allele is found in alpha thalassemia silent carriers. These individuals typically have no thalassemia-related signs or symptoms.