Sickle cell disease (SCD) is a group of genetic disorders that affect the production of red blood cells. More specifically, SCD affects the production of hemoglobin. Hemoglobin is a protein that is one of the main components of red blood cells. As red blood cells travel through the lungs, hemoglobin attaches to oxygen molecules. This enables red blood cells to carry oxygen to tissues and organs throughout the body. Hemoglobin also carries carbon dioxide to the lungs so it can be exhaled.
When a person has SCD, the body produces abnormally shaped hemoglobin that changes the shape and structure of the red blood cells that contain it. Instead of the normal, round shape, red blood cells will have a crescent, or sickle-like shape. This shape is what gives sickle cell disease its name.
What are the symptoms of SCD?
As sickle-shaped red blood cells travel through the body, they can become stuck in the small blood vessels and block blood flow. This can cause episodes of severe pain, damage to organs, recurring infections, anemia, and other problems. The severity of SCD can vary widely from person to person. Some people experience mild symptoms and health problems, while others experience severe symptoms and complications that require hospitalization.
What causes SCD?
SCD is an inherited genetic disorder. It’s caused by genetic variants that a person inherits from their biological parents. A genetic variant is also called a mutation.
- The mutations that cause SCD affect the HBB gene.
- This gene contains instructions for making a protein called beta-globin, which is one of the main components of hemoglobin.
- Different mutations to the HBB gene can produce a variety of abnormal versions of beta-globin or low levels of beta-globin. This results in abnormally shaped hemoglobin, which results in sickle cells.
Each person has two copies of a gene, one inherited from their biological mother and one inherited from their biological father. For a person to have SCD, both biological parents must have a variant HBB gene (though it does not need to be the same variant). This pattern of inheritance is known as autosomal recessive inheritance. A person with one variant copy of the HBB gene will usually not have symptoms of SCD, but they can pass this gene on to their biological children.
What are the treatment options for SCD?
In most cases, treatment for SCD focuses on controlling and managing the condition, including preventing episodes of pain, treating complications, and preventing infections. Therapies used to manage SCD include:
- Medications. There are a variety of medications that treat SCD. This includes medications to reduce the formation of sickle cells, medications to prevent or treat pain, and medications to improve blood flow.
- Blood transfusions. Blood transfusions may be given to increase the number of healthy red blood cells. This may be done to treat and prevent complications, including serious complications like stroke and organ failure.
- Preventing infections. People with SCD are at risk for serious illness from infections like the flu, pneumonia, meningitis, and COVID. This is especially true for children. Vaccines are an essential part of healthcare for people with SCD. Additionally, some children may be prescribed penicillin to prevent infections.
- Avoiding triggers. Dehydration, hot environments, cold environments, fatigue, stress, and trauma can trigger episodes of pain and symptoms, and avoiding these triggers is another part of managing SCD. A healthy lifestyle and lowering stress are also recommended.
Bone marrow transplant
A bone marrow transplant (also called a stem cell transplant) is a procedure that can potentially cure SCD. It is not widely used, as it requires a well-matched donor, chances of success can vary, and there is a risk of serious complications. A bone marrow transplant requires specialized care and hospitalization, as a person must undergo chemotherapy and/or radiation therapy to eliminate existing stem cells in the bone marrow and prepare the body to receive the transplant.
Gene therapy
Several gene therapies are available to treat SCD. Gene therapies work by targeting the underlying cause of SCD—genetic mutations. Gene therapies add modified genes to the body or alter a person’s genes. These are delivered in the form of modified blood-forming stem cells—cells that are collected from a person’s bone marrow, modified in a lab, and then reintroduced into the body. A person will also need to undergo treatment with high doses of chemotherapy to eliminate existing stem cells. Gene therapy is a long, multi-step process that takes roughly a year to complete.
Sources: Centers for Disease Control and Preventi... + 10
- Centers for Disease Control and Prevention. About Sickle Cell Disease.
- National Heart, Lung, and Blood Institute. What Is Sickle Cell Disease?
- Mount Sinai Health Library. Hemoglobin.
- MedlinePlus. Sickle Cell Disease.
- MedlinePlus. What is a gene?
- NCI Dictionary of Genetics Terms. Autosomal recessive inheritance.
- National Heart, Lung, and Blood Institute. Sickle Cell Disease Treatment.
- Centers for Disease Control and Prevention. Complications of SCD: Infection.
- National Organization for Rare Disorders. Sickle Cell Disease.
- National Human Genome Research Institute. Sickle cell disease gene therapy FAQ.
- Carrie MacMillan. Casgevy and Lyfgenia: Two Gene Therapies Approved for Sickle Cell Disease. Yale Medicine. December 19, 2023.
