The sickle cell mutation is the same in all people with sickle cell disease: a conversion of ß-6 glutamic acid to valine. However, the DNA surrounding the ß-globin gene varies, and this forms the "haplotype background". A sickle mutation that occurs in a particular background continues to have that same background in future generations.
Analysis of the sickle gene in different regions of Africa and the Middle East showed that the gene arose several times independently. The haplotypes are named for the geographic regions where they were identified: Senegal, Benin, Central African Republic (CAR) and Asian (Middle East).
The sickle genes arose as a protection against malaria. Later, they spread over much of the world with migration. In India, the Asian haplotype is found almost exclusively. In the Americas, primarily the three major African haplotypes exist. Most people in the new world who have sickle cell disease have two haplotypes, one for each chromosome with the sickle cell gene. Most of the information on the behavior of the homozygous form of the sickle haplotypes were derived from studies in Africa and the Middle East.
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