Sickle cell disease (SCD) is a group of conditions that cause red blood cells to malfunction. Sickle cell anemia is a type of SCD.
Healthy red blood cells are disc-shaped and flexible, which helps them move through blood vessels and deliver oxygen to the body’s cells.
In sickle cell anemia, these red blood cells are crescent- or sickle-shaped, inflexible, and sticky. These traits make them clump together, blocking blood vessels and impairing blood flow. The sickle cells also die early, resulting in a shortage of red blood cells.
This article outlines the different types of SCD. We also describe the symptoms, causes, and treatment options of sickle cell anemia.
Red blood cells contain a protein called hemoglobin, which delivers oxygen to the body’s cells. In all forms of SCD, the red blood cells have an abnormal type of hemoglobin. Doctors refer to this as sickle hemoglobin or hemoglobin S.
Besides hemoglobin S, there are other abnormal variants of hemoglobin. The type of SCD a person has depends on which abnormal hemoglobin genes they inherit from their parents.
Below are the three most common types of SCD.
Sickle cell anemia
Sickle cell anemia is the most common and severe type of SCD. It develops when a person inherits two hemoglobin S genes — one from each parent.
People with sickle cell anemia become anemic. This means that their body does not produce enough red blood cells to supply sufficient oxygen to their cells.
Sickle-hemoglobin C is a milder form of SCD. It occurs when a person inherits two different types of abnormal hemoglobin genes: one for hemoglobin S, and one for hemoglobin C.
Hemoglobin C causes milder symptoms than sickle cell anemia. As a result, a person with sickle-hemoglobin C usually has a higher red blood cell count and a reduced risk of developing anemia than someone with sickle cell anemia.
Sickle beta-plus thalassemia
Sickle beta-plus thalassemia occurs when a person inherits one gene for hemoglobin S and one gene for beta thalassemia.
Beta thalassemia is a different type of anemia, and the gene comes in two forms: 0 and +. Those with the 0 variant usually have a more severe illness than those with the + variant.
Less common types
Below are the rarer types of SCD.
Sickle-hemoglobin D occurs when a person inherits one gene for hemoglobin S and one gene for hemoglobin D. The two genes interact in a way that usually results in mild to moderate anemia. People with one of each gene may also experience bouts of pain.
Sickle-hemoglobin O occurs when a person inherits one gene for hemoglobin S, and one gene for hemoglobin O. The two genes interact to trigger various symptoms ranging from mild to severe.
People with sickle cell trait (SCT) inherit one sickle cell gene from one parent and one normal gene from the other. A person with SCT can pass the trait on to their offspring. If both parents have SCT, there is a 50% chance that their child will inherit the condition and a 25% chance that they will inherit SCD.
Most people with SCT live a normal life without showing symptoms of the disease. In some rare cases, people with the condition may experience health complications following overexertion or dehydration.
When people with SCT exert themselves without training or for extended periods, they may develop a life threatening condition called rhabdomyolysis. This causes muscle breakdown and organ damage. While this phenomenon is more common among people with SCT, it is still very rare.
SCD is a genetic disorder. There is no way to prevent it, though parents may undergo genetic testing and use the results to make reproductive decisions.
The specific type of SCD a person has depends on the genes they inherit. Lifestyle or other external factors do not have a bearing.
While people inherit SCD, certain factors can trigger a sickle cell crisis. This is where sickled red blood cells clump together and block blood vessels, causing dull, throbbing, or stabbing pains in the body. Some people with SCD find that dehydration, infection, stress, or temperature changes trigger sickle cell crises.
SCD symptoms may vary from person to person. Some people feel healthy most of the time and only experience symptoms during a sickle cell crisis. Others frequently feel weak or sick.
Although SCD is present from birth, most infants do not experience symptoms until they are 5–6 months old.
Some common symptoms of SCD include:
- jaundice, a yellowing of the skin and whites of the eyes
- damaged blood vessels in the eyes
- swelling of the feet or hands
- chronic pain
- sudden bouts of pain
- low energy
- fussiness in babies
- recurring infections
- strokes or blood clots
People with SCT do not normally experience any symptoms. However, some notice blood in their urine, usually after extreme exercise or dehydration.
Sickle cell anemia is an inherited condition. A person acquires the genes that cause SCD from each of their parents. Choices during pregnancy or childbirth do not affect the genes that cause SCD, nor any other lifestyle factor.
Sickle cell anemia affects roughly 100,000 people in the United States and is much more common among Black Americans. Approximately 1 in 365 Black or African American babies are born with sickle cell anemia, and 1 in 13 are born with SCT.
Research suggests that SCT may provide some protection against malaria. Therefore, some experts suggest that SCT and associated SCD evolved in humans who had the greatest exposure to malaria.
Doctors often detect SCD at birth during routine blood tests in newborns.
Some people may suspect they have SCD based on family history or symptoms. If they do not have a diagnosis, a blood test can determine if the condition is present, along with its specific subtype.
In 2019, the Food and Drug Administration (FDA) approved the drug Voxelotor to prevent red blood cells from sickling and clumping together. The organization also approved the drug Crizanlizumab-tmca to reduce the severity and frequency of sickle crises.
Other treatment options for SCD include:
- Penicillin: Antibiotics may reduce the risk of certain infections in children with SCD.
- Hydroxyurea: A drug that may reduce the severity of several SCD complications, including:
- pain crises
- acute chest syndrome
- Blood transfusions: A medical procedure that takes blood from a healthy donor and transfers it to a recipient via intravenous injection. Doctors sometimes recommend blood transfusions to help prevent or treat SCD complications.
People with SCD have a life expectancy of around 54 years. However, this figure does not consider the role of treatment and the differences between types of SCD.
Strategies to manage SCD are improving. With appropriate techniques, many people with the condition can lead long and relatively healthy lives.
Doctors usually diagnose sickle cell anemia shortly after birth. However, babies born outside of the hospital or whose parents decline newborn screenings may not receive an early diagnosis.
A person should see a doctor if:
- they and their partner have confirmed or suspected SCT and want to discuss their risk of passing the disease on to their child
- a baby or any other person has symptoms of SCD, especially if there is a family history of the disease
- sickle cell symptoms appear in a child diagnosed with SCD
People should also see a doctor if they experience new or worsening sickle cell symptoms, or if sickle cell treatment does not work. Most people with SCD have an ongoing relationship with a doctor who specializes in blood disorders.
SCD is an inherited chronic condition. A person is born with SCD if they receive a gene for the disease from each of their parents.
In addition, the condition typically requires ongoing treatment. However, the disease’s symptoms and severity vary depending on the type and other individual factors.
A person with sickle cell anemia or another type of SCD should work closely with their doctor to devise an appropriate treatment plan. By following this strategy, they can reduce the risk of health complications.