People who have sickle cell disease inherit two abnormal hemoglobin genes—one from each parent. At least one of the two abnormal genes causes a person’s body to make hemoglobin S.
There are three main types of sickle cell disease:
Hemoglobin SS
Hemoglobin SS disease, also known as sickle cell anemia, is the most common and most severe type of sickle cell disease. It occurs when a child inherits one hemoglobin S gene from each parent.
People with sickle cell anemia have mostly hemoglobin S in their red blood cells. They do not have any hemoglobin A.
Hemoglobin Sβ thalassemia
This form of sickle cell disease has two types:
- sickle beta zero thalassemia disease
- sickle cell beta plus thalassemia disease
Sickle beta zero thalassemia disease
Similar to hemoglobin SS, people with sickle beta zero thalassemia disease have mostly hemoglobin S but have no hemoglobin A. They inherit a sickle cell gene from one parent and a beta thalassemia gene from the other. Beta thalassemia is a disorder that reduces the body’s ability to produce hemoglobin.
A person with this type of sickle cell disease typically can have the same types of symptoms and medical complications as someone with hemoglobin SS disease. Since these two types have the same symptoms and are hard to tell apart without special blood tests, medical doctors and researchers often group them together and call them sickle cell disease.
Sickle beta plus thalassemia disease
People with sickle beta plus thalassemia disease have mostly hemoglobin S, but they also produce a small amount of normal hemoglobin A. They can have symptoms and medical complications like people with Hemoglobin SS, but the presence of hemoglobin A may protect them from certain complications. For instance, they normally do not have strokes as a complication of the disease.
Hemoglobin SC disease (sickle-hemoglobin C disease)
People with hemoglobin SC disease have both hemoglobin S and hemoglobin C in their red blood cells. They inherit a sickle cell gene from one parent and a hemoglobin C gene from the other.
Normally, hemoglobin C alone does not cause many problems, but when a person has it along with hemoglobin S, their red blood cells can still sickle. Someone with hemoglobin SC disease typically has similar symptoms and complications to someone with sickle beta plus thalassemia disease.
