The disease occurs when a person inherits two sickle cell genes or a combination of one sickle cell gene plus any one of several other abnormal hemoglobin genes. Hemoglobin in the red blood cells carries oxygen from the lungs and takes it to every part of the body. The main hemoglobin in the red blood cells of people with sickle cell disease is different from the usual hemoglobin. Red blood cells containing mainly normal hemoglobin are round and flexible. But when oxygen is released by the red blood cells in people with sickle cell disease, the abnormal hemoglobin forces the cells to become distorted and rigid, often looking like the C-shaped farm tool called a sickle.
Sickle cells tend to become trapped and to be destroyed in the liver and in the spleen.
This results in a shortage of red blood cells, or anemia which, when severe, can cause an affected person to be pale, short of breath and easily tired. Certain conditions, such as enlargement of the spleen and infections, may worsen the anemia by speeding up destruction of red blood cells. Infections also can reduce red blood cell production. There are several forms of sickle cell disease. The effects of sickle cell disease vary greatly from one person to the next.