Distribution and Incidence

Sickle-cell anemia is found in as many as 4 percent of Africans and in 1 percent of black Americans (1 per 500). Upward of 40 percent of Africans carry the sickle-cell trait as compared to 9 percent of black Americans. In some Mediterranean cultures the trait is also present. It is now generally believed that the sickle-cell gene mutation occurred independently in several areas of Africa. Therefore, its presence across several different peoples is easily explained.

Hemoglobin S is transmitted as an autosomal recessive gene. So if both parents have sickle-cell trait, the chances are 1 in 4 that any child born to them will have hemoglobin SS and thus sickle-cell anemia; 1 in 4 that it will have hemoglobin AA and be normal; and 2 in 4 that it will have hemoglobin AS and have the sickle-cell trait.

The pattern of death in persons who have sickle-cell anemia is bimodal, with the first peak occurring in childhood and the second occurring among people in their late 30s. Deaths during childhood are related to infectious causes, whereas those during adulthood are due to organ failure from repeated tissue destruction.

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