Sickle cell disease (SCD) is a genetic condition that a person inherits from their biological parents. It is an autosomal recessive condition, meaning that for someone to get SCD, they have to inherit a gene that causes it from both parents.

There are several types of SCD. Each type occurs due to a different combination of genes.

For example, when a person has two copies of hemoglobin S — one from each biological parent — they get sickle cell anemia. This is the most severe form of SCD. Other forms of SCD are less severe but can still cause various symptoms that affect a person’s life.

In this article, learn more about how people inherit SCD, the genes that cause it, and testing and treatment methods.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Every person has two copies of the gene that tells the body how to make hemoglobin. Most people have two copies of hemoglobin A, which leads to the creation of healthy red blood cells.

However, people with sickle cell trait have one copy of hemoglobin A and one copy of another gene that negatively affects blood production. The most common are:

  • hemoglobin S
  • hemoglobin C
  • HBB

Rarely, people carry much less common genes known as hemoglobin D, E, or O. Having just one copy of one of these genes does not usually make a person sick.

Individuals inherit the sickle cell trait from one of their parents. The only difference between having only the genetic trait and having the disease is that instead of inheriting two sickle cell genes, they inherit one.

For a child to inherit SCD, both parents must have sickle cell trait. This means they each carry one copy of a gene that can contribute to the disease. These genes carry atypical genetic instructions for making blood, leading to the production of unhealthy red blood cells.

Several gene combinations can result in SCD, including:

  • HbSS: With this combination, a person inherits one hemoglobin S gene from each parent, which results in sickle cell anemia. This is usually the most severe form of SCD.
  • HbSC: This occurs due to a person inheriting one copy of the hemoglobin S gene and one copy of hemoglobin C. Both of these genes negatively affect hemoglobin production, but less severely than when someone has two copies of hemoglobin S.
  • HbS beta-thalassemia: This occurs when a person inherits hemoglobin S from one parent and beta-thalassemia from the other. Beta thalassemia is another genetic condition that affects hemoglobin. Usually, this type of SCD is milder than others.

There are also some rarer types of SCD people can get, such as:

  • HbSD, which occurs when a person has one copy of hemoglobin S and one copy of hemoglobin D
  • HbSE, which occurs when an individual inherits hemoglobin S and hemoglobin E
  • HbSO, which occurs when a person has hemoglobin S and hemoglobin O

Not all children whose biological parents have sickle cell trait will inherit these genes. If only one parent has sickle cell trait, any child they have has a 50% chance of also having it.

If both parents have sickle cell trait, any child they have has a:

  • 1 in 4 likelihood of not inheriting any sickle cell genes or having SCD
  • 1 in 4 likelihood of inheriting the gene from both parents and having SCD
  • 1 in 2 likelihood of inheriting one copy of the gene from one parent and being a carrier

Unlike some other genetic conditions, parents of any sex can pass on sickle cell genes to a child.

A simple blood test can determine whether or not a person has sickle cell trait or SCD. The test forms part of newborn screening at hospitals in the United States. This means doctors can usually identify it at birth.

Doctors can also diagnose some cases before birth. This is using via two diagnostic tests: chorionic villus sampling and amniocentesis.

Chorionic villus sampling involves analyzing a tiny piece of the placenta to test the fetus’s genes and chromosomes. Amniocentesis is similar but involves the doctor taking a small sample of amniotic fluid that surrounds the fetus.

Stem cell transplants are the only Food and Drug Administration (FDA)-approved treatments that can potentially cure SCD.

This procedure involves killing unhealthy red blood cells via chemotherapy and then replacing them with healthy stem cells from a donor. Doctors get these cells from bone marrow. Ideally, the donor needs to be a sibling of the individual.

However, this treatment has serious side effects, and not everyone is eligible. Doctors usually reserve it for children with severe forms of the disease but whose organs are not yet damaged.

Other treatments for SCD help people reduce symptoms, prevent complications, and live longer with the disease. Often, this includes a combination of medications and lifestyle interventions.

The available medications for SCD include:

  • hydroxyurea for people aged at least 9 months old
  • L-glutamine for people aged at least 5 years
  • voxelotor for people aged at least 12 years
  • crizanlizumab for people aged at least 16 years

Lifestyle interventions focus on preventing sickle cell crises. They include:

  • drinking plenty of fluids
  • wearing warm clothes
  • avoiding sudden changes in temperature, such as swimming in cold water
  • avoiding high altitudes, including flying in planes
  • avoiding low-oxygen environments
  • avoiding intense exercise

As people with SCD are more susceptible to infections, they should ensure that they wash their hands often and prepare food safely. Doctors may also recommend antibiotics and additional vaccinations for children as a preventive measure.

There is much to learn about SCD and the risks of passing on the genes that cause it. Some questions a person may want to ask their doctor include:

  • Do I have sickle cell trait?
  • Could I pass SCD on to any children I have?
  • What is the risk of passing it on?
  • Should I have genetic counseling before trying for a baby?
  • How soon can you test for SCD?

SCD is a genetic condition that children can inherit when both of their biological parents have sickle cell trait. Parents of any sex can pass these genes on.

If only one parent carries a sickle cell gene, the child may inherit sickle cell trait. People with sickle cell trait do not usually experience symptoms. However, they may get them when the body is under stress, such as during intense exercise.

Currently, only a stem cell transplant has the potential to cure SCD. Other treatments focus on reducing symptoms and complications and prolonging life.