What Factors Affect the Frequency of Sickle Cell Anemia?

Sickle cell anemia is a genetic disease characterized by DNA mutations that cause changes in the hemoglobin found in red blood cells. The name sickle cell anemia comes from the sickle shape red blood cells take on as a result of the disease. Primarily, the disease affects only those individuals whose ancestors came from certain regions, such as Africa, Saudi Arabia, and some Mediterranean countries. Factors that influence the frequency of sickle cell anemia include geography, the prevalence of malaria, and the genetics of an individual’s parents and recent ancestors.

Since this particular mutation is a genetically inherited disease, the primary factor affecting the frequency of sickle cell anemia is genetics. Both parents must carry the mutation for a child to have the disease. Parents may have the disease or merely be carriers of the sickle cell trait. According to studies, a child born to parents who both have the defective gene have a 25 percent chance of getting sickle cell anemia and a 50 percent chance of becoming a carrier.

Geography plays an important role in the frequency of sickle cell anemia. Tropical and subtropical regions, especially sub-Saharan Africa, have the highest percentage of people affected. For example, in Nigeria it is estimated that as much as 40 percent of the population are carriers of the mutated gene. Such rates increase the frequency of sickle cell anemia because it is more likely that both parents will carry the gene.

While statistics show that certain regions of the world have higher rates of sickle cell disease, the types of sickle cell anemia seen in certain regions vary. Residents of Saudi Arabia and Senegal, for example, typically present with a more mild form of sickle cell anemia then residents in Africa. Scientists explain these differences because different peoples experienced different spontaneous mutations in the genes linked to sickle cell anemia. Historically, residents of a particular geographic region remained close to ancestral homes, preventing the comingling of genetic mutations or the spread of certain types of mutations to other regions.

Aside from genetics, the biggest factor contributing to the frequency of sickle cell anemia is the prevalence of malaria in a particular region. Malaria is caused by a parasite that resides, at least for a time, in red blood cells. Sickled cells cannot support the parasite and typically die before the parasite can replicate. In many regions, this inherited resistance to malaria provides the population with a built-in defense. Unfortunately, the result is a higher frequency of sickle cell anemia among residents, since more people with the mutation are able to survive an outbreak.