Sickle cell anaemia is a part of a group of diseases referred to as sickle cell disease or SCD for short. These are diseases that affect the haemoglobin in the body,  the molecule within red blood cells that are responsible for the delivery of oxygen. All SCDs are inherited genetically and are present at birth. With 2 parents that carry the trait, there is a 1 in 4 chance that the child will suffer from the disease and a 50% chance that they will just be a carrier. 

This group of diseases is extremely prevalent in West Africa and common in places like South Asia as well. With research into DNA polymorphism, or simply put, the variants of a specific DNA sequence, scientists were able to pinpoint where the disease’ trait stemmed from. The polymorphism of the beta S gene showed evidence of the disease stemming from 5 separate mutations, four of which originated in West Africa. 

In the United States, the sickle cell trait is present in approximately 8% of the black population, which is approximately 3.4 million people. This figure seems small when we compare the value to that of Africa, where the preponderance can be up to 30%. 

References:

https://www.news-medical.net/health/Sickle-Cell-Disease-History.aspx