About 8-10 per cent of all African Americans carry the sickle cell gene. The remainder or about 1 in 500 are homozygous for hemoglobin S and actually have sickle cell disease and suffer from the effects of hemolysis. Sickle cell disease is a serious, hereditary, chronic disease in which the red blood cells have reduced life span and are rigid, with a crescent or sickle shape. The shape is the result of an abnormality in the hemoglobin, which alters the deformability of the red cells under conditions of low oxygen tension. Because of their distorted shape the red blood cells have difficulty passing through the small arterioles and capillaries and have a tendency to clump together and occlude the blood vessel.
Some scientists believe that sickle cell disease developed as a defense against malaria.
There are many symptoms of sickle cell disease, all of them related to the defective hemoglobin and its effect on the red blood cells. Some persons with the disease suffer from only a few symptoms, while others are severely affected and have a short life span. Very few severely affected persons live beyond the age of 20, and some die in infancy or early childhood. The major symptoms are anemia, periodic joint and extremity pain and sometimes edema of the joints, chronic ulceration about the ankles, episodes of severe abdominal pain with vomiting, and abdominal distention. The spleen becomes infarcted so that it is essentially absent and predisposes the patient to infection with encapsulated organisms.