What Is Sickle Cell Anemia?
Sickle cell anemia, known medically as HbSS, is a type of inherited red blood cell disease. It is one of the most common among a group of inherited red blood cell disorders that are broadly labeled as sickle cell disease. People with sickle cell anemia inherit two sickle cell genes, one from each parent.1
Red blood cells are typically flexible and round, allowing them to glide through blood vessels. In sickle cell anemia, blood cells take on a crescent moon or sickle shape. This problem stems from hemoglobin, a molecule that’s critical for transporting oxygen in the blood.2
In sickle cell anemia, hemoglobin is called hemoglobin S. This type of hemoglobin is caused by a mutation in the hemoglobin beta gene (HBB), which gives sickle cell hemoglobin its abnormal shape.1,3,4
Human blood cells pass through body tissues, allowing those tissues to absorb most of the oxygen they carry.1 But rather than passing through smoothly like healthy blood cells, sickle cells become sticky and clump together, because sickle cell hemoglobin forms stiff protein rods inside the red blood cells. These bend the cells into their characteristic sickle or C shape.1,2,3
As these blood cells become rigid, they’re also more likely to burst or stick to each other, as well as other cells. This can obstruct blood flow.2,5
These obstructions can lead to intense periods of pain, called pain crises, which can last for hours or even days. These red blood cell changes can also cause another problem: anemia.2,5
Red blood cells typically have a lifespan of about 120 days before the body replaces them. Sickle cells, however, tend to have a 10-to-20-day lifespan. This can leave the body chronically short on red blood cells—a condition called anemia. Insufficient red blood cells leave the body oxygen-starved, which can lead to fatigue and can contribute to organ damage and dysfunction.1,5
Some treatment for anemia in people with HbSS can lead to high iron levels in the blood, which can damage organs.1
Children with sickle cell anemia sometimes experience splenic sequestration crises in the first decade of their lives. In a splenic sequestration crisis, the spleen becomes engorged with trapped blood, which lowers the amount of blood circulating elsewhere in the body, posing risk to the child.1,6,7
Over time, the spleen may shrink from these crises. But sometimes it doesn’t, requiring surgical removal of the spleen. This can lead to risks of infection.1,6,7
Prevalence of Sickle Cell Anemia
The precise number of people in the U.S. with sickle cell disease is difficult to pinpoint, but estimates range between 100,000 and 200,000.3,8 Sickle cell disease predominantly affects people with sub-Saharan African ancestry. It also occurs in people with Hispanic, South Asian, Southern European, and Middle Eastern ancestry.8 There are many types of sickle cell disease, but the most severe is sickle cell anemia.1
Sickle Cell Trait vs. Sickle Cell Disease
Having sickle cell trait does not mean you have sickle cell disease or, specifically, sickle cell anemia. With sickle cell trait, you inherit one sickle cell gene from one parent and a normal hemoglobin gene from your other parent.1 Approximately 1 in 13 Black people is born with sickle cell trait.1,8
The healthy hemoglobin in people with sickle cell trait functions well enough to prevent red blood cells from taking on the C shape. Consequently, people with sickle cell trait don't show any signs of sickle cell disease or anemia and can live normal lives. However, they can pass the gene on to their children. If two parents have sickle cell trait, each of their children has a 25% chance of inheriting sickle cell disease, which may include sickle cell anemia.9
Sickle Cell Anemia in Children
Sickle cell anemia is present at birth. Children will inherit the condition when they receive a sickle cell gene from each parent. Symptoms typically appear around 5 months of age.2