This is the fourth part of our series about the condition based on our patient booklet “Fast Facts for Patients: Alpha Thalassemia”. This article focuses on three gene changes in alpha thalassemia.

If you have three gene changes, you have Hemoglobin H AT (HbH AT).

What Does This Mean?

The symptoms and complications you experience will depend on the type of gene change you have.

People with non-deletional HbH tend to have more severe disease than people with missing AT genes (deletional HbH).

You may have only mild anemia or it may be severe enough for you to need regular blood transfusions from a young age.

What Is the Risk If I Have Children?

If one parent has three gene changes but the other parent has no changes, for each pregnancy there is a:

• 1 in 2 chance (50%) the baby will be a carrier (one gene change)
• 1 in 2 chance (50%) the baby will have AT trait (two gene changes on the same chromosome).

If one parent has three gene changes and the other has one gene change, for each pregnancy there is a:

• 1 in 4 chance (25%) the baby will be a carrier (one gene change)
• 1 in 2 chance (50%) the baby will have AT trait (two gene changes)
• 1 in 4 chance (25%) the baby will have HbH AT (three gene changes).

If one parent has three gene changes and the other has two gene changes on the same chromosome, for each pregnancy there is a:

• 1 in 4 chance (25%) the baby will be a carrier (one gene change)
• 1 in 4 chance (25%) the baby will have AT trait (two gene changes on the same chromosome)
• 1 in 4 chance (25%) the baby will have HbH AT (three gene changes)
• 1 in 4 chance (25%) the baby will have AT major (four gene changes).

If one parent has three gene changes and the other has two gene changes, one on each chromosome, for each pregnancy there is a:

• 1 in 2 chance (50%) the baby will have AT trait (two gene changes changes, one on each chromosome)
• 1 in 2 chance (50%) the baby will have HbH AT (three gene changes).

If both parents have three gene changes, for each pregnancy there is a:

• 1 in 4 chance (25%) the baby will have AT trait (two gene changes on the same chromosome)
• 1 in 2 chance (50%) the baby will have HbH AT (three gene changes)
• 1 in 4 chance (25%) the baby will have AT major (four gene changes).

Please check out the other posts of our series here:

• What Is Alpha Thalassemia?
• Alpha Thalassemia: Genes, Genetic Inheritance and One Gene Change
• Alpha Thalassemia: Two Gene Changes
• Alpha Thalassemia: Four Gene Changes
• Alpha Thalassemia: Screening and Diagnosis
• Alpha Thalassemia: Symptoms and Treatment
• Alpha Thalassemia: Clinical Trials and New Treatments
• Living with Alpha Thalassemia

Information based on Fast Facts for Patients: Alpha Thalassemia (Karger, 2023).