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Sickle cell disease (SCD) can bring up a lot of questions. You may wonder how you or your child ended up with it, whether it could show up again in future children, or if other people in your family might be carriers without knowing it.
But getting those answers can sometimes be challenging. Some people may not know their family’s sickle cell history, may not have access to previous test results, or may face barriers to genetic or hemoglobin testing. Past experiences with screening or the healthcare system can also affect how comfortable someone feels seeking testing or counseling.
Sickle cell disease is caused by inherited gene changes that affect hemoglobin (a protein in red blood cells). Read on to learn how it’s inherited and how it can be passed down from parents to children.
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A child can inherit sickle cell disease only if they receive a gene linked to abnormal hemoglobin from each biological parent.
These inherited gene changes, called variants or mutations, affect how the body makes hemoglobin. Instead of typical hemoglobin, the body produces hemoglobin S — an altered form that can cause red blood cells to become stiff and sickle-shaped instead of round and flexible.
Sickle-shaped cells can block blood flow and break down faster than healthy red blood cells. This increases the risk of complications such as:
Sickle cell trait (SCT) and sickle cell disease are both inherited conditions involving hemoglobin, but they are distinct from one another.
People with sickle cell trait inherit one gene variant that produces hemoglobin S and one typical hemoglobin gene. People with sickle cell disease inherit a variant that produces hemoglobin S from one biological parent and another SCD-associated hemoglobin gene variant from the other. The second variant may also produce hemoglobin S or hemoglobin C, or it may be a beta-thalassemia variant or another less common hemoglobin variant.
Because people with sickle cell trait have one typical hemoglobin gene, most don’t have symptoms. Under extreme conditions, however, some of their red blood cells may sickle. These conditions may include:
Even without symptoms, a person with sickle cell trait can pass the hemoglobin S variant on to their children. People with sickle cell disease, on the other hand, are more likely to experience symptoms and complications.
Some people with sickle cell trait don’t know they have it until they’re tested or until a child in the family is diagnosed. Not knowing your status doesn’t mean you did anything wrong.
The three most common types of sickle cell disease are HbSS, HbSC, and HbS beta-thalassemia, although rarer types also occur. A person’s type depends on which hemoglobin gene variants they inherit from each biological parent.
Hemoglobin SS (HbSS), also known as sickle cell anemia, is the most common type of sickle cell disease and is often associated with greater severity. A person with HbSS inherits a variant that produces hemoglobin S from each biological parent.
People with HbSS may experience frequent pain episodes, anemia, and other complications of sickle cell disease.
HbSC occurs when a person inherits a hemoglobin S gene variant from one parent and a hemoglobin C gene variant from the other. Symptoms may be less severe than with HbSS, but HbSC can still cause serious complications, and disease severity varies from person to person.
This type occurs when a person inherits one hemoglobin S gene variant from one parent and a beta-thalassemia gene variant from the other. There are two main forms: HbS beta-zero and HbS beta-plus. Symptoms can range from mild to severe, depending on the type of beta-thalassemia that’s inherited.
Less common types include hemoglobin SD (HbSD), hemoglobin SE (HbSE), and hemoglobin SO (HbSO). These occur when a person inherits a hemoglobin S gene variant along with another less common hemoglobin variant.
If you’re not sure which type of sickle cell disease you or your child has, don’t hesitate to ask your healthcare provider. They can review your medical records or order testing to confirm the type.
People with ancestry from certain parts of the world are more likely to carry a hemoglobin S gene variant associated with sickle cell trait and sickle cell disease. According to the National Heart, Lung, and Blood Institute, these regions include:
In the United States, an estimated 8 percent to 10 percent of African Americans have sickle cell trait, according to the American Society of Hematology.
However, sickle cell trait and sickle cell disease aren’t limited to any one racial or ethnic group. Having ancestry from one of these regions doesn’t mean that a person will have sickle cell trait. People from other backgrounds can carry hemoglobin variants as well.
The hemoglobin S gene variant became more common in regions where malaria has historically been widespread. This is because having sickle cell trait can provide some protection against severe malaria.
Since ancestry alone can’t tell you for certain whether you carry the gene, a blood test can help you understand your status.
Having a family history of sickle cell disease or sickle cell trait may increase the chance that you carry a hemoglobin variant associated with SCD. Family history can be helpful, but it doesn’t always provide the full picture.
Some relatives may not know their hemoglobin status, may not feel comfortable talking about it, or may not have had access to testing.
Knowing the hemoglobin types of both biological parents can help determine a child’s chances of inheriting sickle cell trait or sickle cell disease. Here are two common scenarios.
When both biological parents have sickle cell trait, each pregnancy has:
Because people with sickle cell trait usually don’t have symptoms, carriers may not know their status unless they’re tested.
When one biological parent has HbSS sickle cell disease and the other has sickle cell trait (HbAS), each pregnancy has:
Because the parent with HbSS has two hemoglobin S gene variants, every child will inherit one of those variants from that parent.
These chances may be different if the parent has another type of sickle cell disease, such as HbSC or hemoglobin S/beta-thalassemia. If you’re planning a family or already have children, a genetic counselor can walk you through your specific chances.
Having one child with sickle cell disease doesn’t mean future children are more or less likely to have it. The same chances apply to every pregnancy.
A blood test can identify sickle cell trait, sickle cell disease, and other hemoglobin variants.
In the U.S., newborn screening routinely checks for sickle cell disease and sickle cell trait shortly after birth. Sickle cell disease can also be identified before birth through prenatal diagnostic testing.
But if you weren’t tested at birth or were born before newborn screening became widely available, you can still get tested at any age. Talk to your healthcare provider about which test is appropriate for you.
If you’re planning a pregnancy, your healthcare provider can also offer testing to you and the child’s other biological parent to help you understand your chances of passing a changed hemoglobin gene to the child.
Once you have your results, a genetic counselor can help you make sense of what they mean, both for your own health and for family planning.
However, learning your status isn’t always simple. Some people face barriers that make it harder, such as:
Wherever you’re starting from, you deserve clear information and support. Look for a healthcare provider or genetic counselor who takes the time to listen, explain your options, answer your questions, and respect whatever you decide.
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