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Monday, December 9, 2013
As we've become more knowledgeable about sickle cell anemia we've discovered that it is not infectious but rather genetic. In other words you can't get sickle cell from exposure to a toxin, infection, virus, or parasite. People with sickle cell are born with the disease. It is inherited when parents pass it on to their children.
We've also discovered that sickle cell is, in the United States, very prevalent among dark skinned people and almost completely absent in "white" populations. This is why sickle cell anemia has been, for a very long time, associated with people of dark skin color. This association has been based on the partially correct assumption that sickle cell originates in Africa and those who are of African descent (and therefore very often dark skinned) are the only people who can carry the gene for the disease and pass it on genetically.
While it is true that sickle cell is very prevalent in much of Africa it is entirely untrue that it is confined just to that region. In fact sickle cell is prevalent in parts of all of the following areas:
In each region both dark and light skinned people have been found to be sickle cell carriers. The explanation for this particular distribution lies in explanation for the survival of sickle cell over time.
As has already been explained, sickle cell can for various reasons be a fatal disease. You may think, therefore, that over thousands of years most people without any medical assistance would not survive long enough to reproduce and pass on the sickle cell gene. If people don't live to pass on the gene for the disease wouldn't it disappear? The answer is yes, if there were no other factors, it probably would have. But somehow sickle cell has remained with us despite its self destructive nature. Scientists have discovered that it was another disease, malaria, which made way for the survival of sickle cell.
You may ask – how can one disease help another to survive? What we've discovered is that where malaria is prevalent in the world (in areas that are now or once were hot and humid – ideal breeding grounds for malaria carrying mosquitoes), sickle cell is also prevalent. This is because people who carry sickle cell genes are more resistant to malaria.
Malaria has been around longer than humans have and has always acted on human populations. Therefore, since our beginning, malaria has been 'selecting for' the sickle cell gene (it kills non sickle cell/non malaria resistant people and leaves behind sickle cell carriers to reproduce and pass on the sickle cell gene). This explains why, despite our racial assumptions about sickle cell, the disease is for example rare in South Africa but prevalent in Greece. Sickle cell does not follow dark skin. Sickle cell follows malaria.
This article is a NetWellness exclusive.
Last Reviewed: Jul 10, 2009
Eric H Kraut, MD
Professor of Hematology
College of Medicine
The Ohio State University
Anthony D Villella, MD
Formerly, Assistant Professor of Pediatrics
School of Medicine
Case Western Reserve University