Risk Factors
Sickle cell disease is inherited. People at risk for inheriting the gene for sickle cell descend from people who are or were originally from Africa and parts of India and the Mediterranean. The sickle cell gene also occurs in people from South and Central America, the Caribbean, and the Middle East. The high incidence of the sickle cell gene in these regions of the world is due to the sickle cell's ability to make red blood cells resistant to the malaria parasite:
- People who inherit just a single gene are referred to as having the sickle trait. These people are protected against malaria and do not develop sickle cell disease. About 40% of people in certain parts of Africa and about 9% of African-Americans have the trait.
- Those who inherit both copies of the HbS gene develop sickle cell disease. They are not protected from malaria, however. In fact, malaria is more serious in these individuals. An estimated 1 in 500 African-Americans and 1 in 1,000 - 1,400 Hispanic Americans are born with sickle cell disease.
Risk of Inheritance
The sickle cell gene for hemoglobin S (HbS) is the most common inherited blood condition in the United States. About 70,000 - 100,000 Americans -- mostly African-Americans -- have sickle cell disease. About 2 million Americans have sickle cell trait.
People inherit a pair of genes that regulate hemoglobin, with one gene coming from each parent. If two sickle genes are inherited, a person will have sickle cell disease. If a one normal hemoglobin gene and one sickle cell gene are inherited, a person will have sickle cell trait. People who have sickle cell trait are healthy and do not develop themselves sickle cell disease, but they are 'carriers' who can pass the disease on to their children.
The risk of a child inheriting sickle cell disease or sickle cell trait is as follows:
