Dr. Mason, who observed the fourth reported case of Sickle Cell, was also the first to call the disease “Sickle Cell Anemia” and to notice the similarities between the cases. He also noted that all of these patients were black, inadvertently giving rise to the popular misconception that Sickle Cell originated from people of African origin.
There are two main theories put forward to explain the origin of the Sickle Cell mutation.
- Single Mutation Theory: A single mutation occurring in Neolithic times in the Arabian Peninsula was originally postulated where changing climatic conditions resulted in human migration to India, Saudi Arabia, and down to Equatorial Africa. Evidence for this theory included the distribution of certain agricultural practices and anthropological evidence. Evidence from blood groups and other genetic markers appeared to agree with an origin in Equatorial Africa and subsequent diffusion of the gene to India, Arabia, and the Mediterranean by the East African slave trade.
- Multiple Mutation Theory: The multiple mutation theory has recently gained considerable support via genetic studies with the use of special enzymes called restriction endonucleases. These enzymes recognize and cut DNA at specific sequences. By using these enzymes to cut DNA from a normal individual and an individual with a disease and by looking at the differences between the patterns scientists are able to identify variations in DNA that are inherited. The technique is known as restriction fragment polymorphism mapping. One of the first marker to be looked at was the Beta-globulin gene (the one mutated in SCA) where a difference in the cutting patterns was observed between normal beta-globin genes and the samples that came from SCA patients. These variations identified within the beta-globin gene gives support to the multiple mutation theory. Since there were 4 different mutations, it is believed that these arose at 4 different geographical locations in Africa Benin, Senegal, Central Africa and Cameroon. There’s a 5th mutation that is associated with Eastern provinces of Saudi Arabia and Central India. These observed differences suggest rather than originating from a single origin and spreading across the world that the beta-globin mutation arose at multiple geographical locations independently of each other.
The multiple mutation theory also refutes the misconception of African origin.