What Is Alpha Thalassemia?

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Alpha thalassemia is an inherited anemia where the body is unable to produce a normal amount of hemoglobin. Hemoglobin A (the major hemoglobin in adults) contains two alpha globin chains and two beta globin chains.  In alpha thalassemia, there is a reduced amount of alpha globes.

What Are the Types of Alpha Thalassemia?

  • Alpha thalassemia minima (silent carrier) occurs when one alpha globin gene is lost.
  • Alpha thalassemia minor (or trait) occurs when two alpha globin genes are lost.  There are two forms.  When the two alpha globin genes lost are on the same chromosome 16 is called cis, but when one alpha globin gene is missing on each copy of chromosome 16 this is called trans.
  • Hemoglobin H disease (or alpha thalassemia intermedia) occurs when three alpha globin genes do not function.  In this case, there are an excessive amount of beta globins.  When these join together, it is called Hemoglobin H.
  • Hydrops fetalis occurs when all four alpha globin genes are lost.  Historically, this has been incompatible with life.  If risk is known in advance, intrauterine transfusions (transfusions to the fetus while still in the uterus) may allow for successful delivery. These children require chronic transfusion therapy after birth and often bone marrow transplantation.
  • Hemoglobin H Constant Spring is a variant of alpha thalassemia where two alpha globin genes are lost plus one alpha globin gene is mutated.

    Who Is at Risk for Alpha Thalassemia?

    Alpha thalassemia is commonly associated with Asia, Africa, and the Mediterranean area.  In the US, approximately 30 percent of African-Americans have either alpha thalassemia minima or minor.

    Alpha thalassemia is an inherited condition and requires both parents to be carriers.

     A person without alpha thalassemia should have four alpha globin genes.  The risk of having a child with alpha thalassemia disease is dependent on the status of the parents.  The trans form of alpha thalassemia minor is more common in people of African descent.  The cis form more common in people from Asia or the Mediterranean region.

    If both parents have trans alpha thalassemia minor (a-/a-), all of their children with will have trans alpha thalassemia minor.  If one parent has cis alpha thalassemia minor (aa/--) and the other parent has trans alpha thalassemia minor (a-/a-), they have a 1 in 2 chance of having a child with Hemoglobin H disease. Similarly, If one parent has cis alpha thalassemia minor (aa/--) and the other parent has thalassemia minima (aa/a-), they have a 1 in 4 chance of having a child with Hemoglobin H disease. Hydrops fetalis occurs when both parents have cis alpha thalassemia minor.

    How Is Alpha Thalassemia Diagnosed?

    Alpha thalassemia minima causes no laboratory changes on CBC.

    This is why it is called silent carrier.  This is usually suspected after a child is born with Hemoglobin H disease. This can only be determined by genetic testing.

    Occasionally alpha thalassemia minor is identified on newborn screen, but not in all cases.  The test is positive for Hemoglobin Bart's or fast bands.  Many people with alpha thalassemia minor I have no idea.  This usually comes to light during a routine complete blood count (CBC). The CBC will reveal a mild to moderate anemia with very small red blood cells.  This can be confused with iron deficiency anemia. In general, if iron deficiency anemia is ruled out and beta thalassemia trait is ruled out, the patient has alpha thalassemia trait. If necessary, this can be confirmed by genetic testing.

    Hemoglobin H can be identified on the newborn screen as well. These children are referred to hematologist to be monitored closely. Some patients are identified later in life during work-up of anemia. 

    Hydrops fetalis is not a specific diagnosis, but rather characteristic features on neonatal ultrasound. The loss of four alpha globin genes is found during the work-up for the cause of hydrops.

    What Are the Treatments for Alpha Thalassemia?

    No treatment is needed for alpha thalassemia minima or minor. People with alpha thalassemia minor will have lifelong mild anemia.

    Transfusions: Patients with Hemoglobin H usually have moderate anemia that is well tolerated. Transfuions are needed occasionally during illnesses with fever as the amount of red blood cell breakdown is accelerated. Transfusions may be needed more regularly in adulthood. Patients with Hemoglobin H Constant Spring can have significant anemia and require frequent transfusions during their lifetime.

    Iron chelation therapy: Patients with Hemoglobin H disease may develop iron overload even in the absence of blood transfusions secondary to increased absorption of iron in the small intestine. They can be treated with medications called chelators to help rid the body of excess iron.

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