Hemoglobin types and sickle cell disease
Your red blood cells contain hemoglobin, a protein that carries oxygen. Red blood cells need hemoglobin to deliver oxygen to your body’s organs and tissues. Every red blood cell contains thousands of hemoglobin molecules.
The genes in our body code for different types of hemoglobin. We will focus on three types:
- Hemoglobin F, also known as fetal hemoglobin or HbF, is present in red blood cells before birth (during fetal development). After birth, a gene that codes for a blocking protein (BCL11A) is turned on. BCL11A blocks the production of fetal hemoglobin and tells the body to instead make hemoglobin A. For individuals with sickle cell disease, a small amount of HbF continues to be produced after birth.
- Hemoglobin A, also known as adult hemoglobin or HbA, is typically present in red blood cells after birth.
- Hemoglobin S, also known as sickled hemoglobin or HbS, is an abnormal version of hemoglobin A. Instead of hemoglobin A, the body makes hemoglobin S due to a genetic variant. While hemoglobin S still delivers oxygen, it is not stable and can break apart easily. Hemoglobin S also causes the red blood cells to form a crescent — or sickle — shape.
Sickle cell disease is caused by a genetic variant that makes the body produce hemoglobin S instead of hemoglobin A. You must inherit two variant hemoglobin genes — one for sickle hemoglobin and the other for sickle hemoglobin or another hemoglobin variant (such as hemoglobin C or beta-thalassemia) — to have sickle cell disease. With sickle cell disease, the red blood cells (that are typically round) are sickle-shaped, which causes different health complications.
