What abnormal form of hemoglobin is responsible for sickle cell anemia?

Sickle cell anemia is caused by the presence of an abnormal form of hemoglobin known as hemoglobin S (Hbs). This abnormal hemoglobin leads to the distortion of red blood cells into a sickle shape, particularly when deoxygenated. The sickle-shaped cells are less flexible and can block blood flow in small blood vessels, which results in various complications such as pain crises, increased risk of infection, and organ damage due to reduced blood supply.

Hemoglobin A (Hba) is the normal adult hemoglobin and is not responsible for the disease. Hbc and Hbd refer to other variant hemoglobins that are not implicated in sickle cell anemia.

In summary, the defining characteristic of sickle cell anemia is the presence of hemoglobin S, which significantly impacts the physical properties of red blood cells and contributes to the clinical manifestations of the disease.