Possibly, the defective hemoglobin S-producing gene has persisted because in areas where malaria is endemic, the heterozygous sickle cell trait provides resistance to malaria and is actually beneficial. Figure 1 . Passage of the sickle cell gene from parents to offspring The abnormal hemoglobin S found in such patients' RBCs becomes insoluble whenever hypoxia occurs. As a result, these RBCs become rigid, rough, and elongated, forming a crescent or sickle shape. In addition, these altered cells tend to pile up in capillaries and smaller blood vessels, making the blood more viscous.
Normal circulation is impaired, causing pain, tissue infarctions, and swelling.
Such blockage causes anoxic changes that lead to further sickling and obstruction. Figure 2 . Normal and sickled red blood cells Signs and Symptoms A number of symptoms are associated with sickle cell anemia, and in particular several types of crises. Such symptoms usually don't develop until after 6 months of age, since large amounts of fetal hemoglobin protect infants for the first few months after birth. Low socioeconomic status and related problems, such as poor nutrition and low educational levels, may delay diagnosis and supportive treatment.