Thalassemia trait means you carry the gene that causes the disease, but you don’t have the disease yourself. You likely won’t have symptoms or may have mild symptoms. Still, you can pass on the disease to your child.

Thalassemia is an inherited blood disorder that causes you not to make enough hemoglobin, a protein in your blood. Hemoglobin allows your red blood cells to carry oxygen to other cells throughout your body. Without enough hemoglobin, your red blood cells die more quickly, and your organs and tissues don’t get enough oxygen.

Thalassemia results from an affected gene that causes the problem with hemoglobin. To inherit thalassemia, both your parents must pass down the affected gene to you. If you only receive the gene from one parent, you carry the trait for thalassemia.

Thalassemia trait, aka thalassemia minor, usually doesn’t cause health issues. But you can still pass down the affected gene to future generations.

Thalassemia is an autosomal recessive condition. “Recessive” means that you need two copies of the faulty gene to have the disease. If you have one unaffected gene, it mostly overrides the faulty gene.

“Autosomal” means the affected genes aren’t on sex chromosomes. That means your genetic sex (based on which sex chromosomes you have) doesn’t influence whether you inherit the condition.

Alpha- vs. beta-thalassemia

Several genes contribute to the production of hemoglobin. Most hemoglobin is made up of alpha and beta chains. Some genes contribute to the alpha chain, while others contribute to the beta chain.

Alpha-thalassemia occurs when your body has trouble producing hemoglobin alpha. Beta-thalassemia occurs when your body has trouble producing hemoglobin beta.

It is possible to have both alpha- and beta-thalassemia.

Was this helpful?

There are two types of alpha-thalassemia trait. That’s because two genes, HBA1 and HBA2, are responsible for making hemoglobin alpha.

You inherit two copies of each gene — one from each parent — so four in total. The result will depend on the number of affected genes.

If the inherited mutation affects only one gene, you are a silent carrier for alpha-thalassemia. You can still pass on the affected gene, but you won’t experience any symptoms.

If the mutation affects two genes, you have alpha-thalassemia minor. Your red blood cells are likely to be smaller than is typical. This may cause you to experience mild anemia.

If the mutation affects three of your genes, you have a more severe case of alpha-thalassemia.

Number of affected genesResulting conditionSymptoms
1Alpha-thalassemia silent carrierNone
2Alpha-thalassemia minorNone or very few
3Hemoglobin H diseaseSevere thalassemia
4Hydrops fetalisUsually fatal before or soon after birth

Unlike its alpha counterpart, only one gene (HBB) is responsible for making hemoglobin beta. You inherit two copies of this gene — one from each parent.

In some cases, the inherited mutation can cause the HBB gene to be absent. Scientists use “+” to indicate a gene mutation that lowers production and “0” to indicate a mutation that causes the gene to be absent.

If the inherited mutation affects only one gene, you have beta-thalassemia minor. Like in alpha-thalassemia minor, your red blood cells will be smaller, and you may experience mild anemia.

GenesResulting conditionSymptoms
1 affectedBeta-thalassemia minorNone
2 affected (+)Beta-thalassemia intermediaLess severe thalassemia
2 affected (0)Beta-thalassemia majorSevere thalassemia

How likely am I to pass on thalassemia trait to my child?

If you have beta-thalassemia trait, you have a 50% chance of passing on the affected gene to any child you have.

In general, if both parents have thalassemia trait, there’s a:

  • 25% chance their child won’t have thalassemia trait
  • 50% chance their child will have thalassemia trait
  • 25% chance their child will have a severe form of thalassemia

Because more genes are involved in alpha-thalassemia trait, there are several possible outcomes depending on each parent’s combination of genes.

Was this helpful?

People with thalassemia trait don’t usually have symptoms. If symptoms occur, they’re likely to be mild.

With thalassemia trait, your red blood cells are smaller than those in people who don’t have the trait. This means you have lower levels of hemoglobin, which could result in mild anemia. Possible symptoms include:

Doctors sometimes mistake symptoms of thalassemia trait for iron deficiency.

If you’re a silent carrier or have thalassemia minor, you’re unlikely to need typical thalassemia treatments, like blood transfusions or iron therapy.

Doctors sometimes incorrectly prescribe iron supplements for people with thalassemia trait if they mistake their symptoms for iron deficiency. This could be dangerous, as too much iron can cause serious health problems.

It’s important for a doctor to order a blood test to confirm the cause of your symptoms to ensure you don’t receive any unnecessary treatment.

If you have a family history of thalassemia, you may want to know whether you carry the trait.

A simple blood test known as a complete blood count (CBC) could suggest whether or not you have thalassemia trait. A doctor can look at your mean corpuscular volume (MCV) reading on your CBC results to determine the size of your red blood cells. If your MCV is too low, they may order further blood tests to check for thalassemia trait.

But blood tests can only lead doctors to presume that you have the trait. Genetic testing is the only way to confirm whether you carry the gene. It’s also the only way to tell if you’re a silent carrier. But such tests are often costly.

Newborn screening

Newborn screening tests in the United States don’t specifically check for thalassemia trait. But they do test for sickle cell anemia, which can also detect thalassemia. According to research from 2020 and 2021, 93% of U.S. newborn screening programs provide some info on alpha-thalassemia and 85% provide info on beta-thalassemia.

How common is thalassemia trait?

Some studies estimate the worldwide prevalence of alpha-thalassemia trait to be as high as 5%. It’s most common in Southeast Asia, the Middle East, and the Mediterranean.

Beta-thalassemia trait is less common. Experts estimate 1.5% of the world’s population to be carriers. It’s more common in many of the same parts of the world as alpha-thalassemia. But it’s most common in the Mediterranean, where incidence can be as high as 15%.

Is thalassemia trait life threatening?

Since thalassemia trait causes only mild symptoms, if any, it usually doesn’t affect life expectancy.

Is it possible to carry the trait for both alpha- and beta-thalassemia?

Yes, you can have the trait for both alpha- and beta-thalassemia. A 2014 Chinese study found that 17.8% of people with beta-thalassemia trait also had genetic mutations that affected the alpha gene.

You can also have both alpha- and beta-thalassemia.

Can thalassemia trait affect my pregnancy?

According to the National Heart, Lung, and Blood Institute, thalassemia can affect your ability to become pregnant and increase your risk of complications if you do. But if you only have the trait, you may have a slightly increased risk of high blood pressure or anemia during pregnancy, according to 2022 research.

Learn more about beta-thalassemia trait and pregnancy.

Does thalassemia trait make you more susceptible to COVID-19?

According to the Centers for Disease Control and Prevention (CDC), people with thalassemia may be at increased risk of severe illness from COVID-19. A 2022 study found that people with beta-thalassemia trait were also at increased risk of severe illness from COVID-19.

Learn more about COVID-19 vaccination for people with beta-thalassemia or beta-thalassemia trait.

If you have thalassemia trait, it means you carry a genetic mutation that causes thalassemia, but you don’t have the disease yourself. You likely won’t have any symptoms. If you do, they’ll be mild.

But you can pass the gene on to future generations. If both parents carry a trait for either alpha- or beta-thalassemia, their child could develop a severe form of the disease. So, it’s important to know your status.

A simple blood test could let a doctor know if you have alpha- or beta-thalassemia minor. But some silent carriers of alpha-thalassemia may need a DNA test to know for sure.

Consider talking with a doctor about testing for thalassemia trait if there’s a history of thalassemia or thalassemia trait in your family, or if you plan to have a child with someone who has the trait or a family history of it.