Human geneticist Sarah Tishkoff of the University of Maryland in College Park said the study offers "striking evidence that the HbC provides resistance against malaria." Other studies have shown that in regions where malaria is endemic, genetic mutations have arisen that confer resistance against the disease. This study is valuable because it identifies another gene that provides resistance to malaria.
Malaria is endemic to more than 90 countries, posing a threat to 2.4 billion people.
One puzzling question posed by the new study is why the HbC gene is not more prevalent, said Tishkoff. "If the HbC gene has such a great advantage and provides such high protection against malaria, then you would expect everyone in Africa, or at least Burkina Faso, to have this version of the gene," she said.
The fact that only about one in five people carries the mutant HbC gene suggests there may be some disadvantage associated with this form of the gene, said Tishkoff. Another possibility is that the mutation has arisen relatively recently and has not spread through the population.
"I would be very interested in knowing the age of the [HbC] mutation," which would help determine why HbC isn't more prevalent, Tishkoff said.
Other genetic mutations that protect against malaria are not common in malaria-prone regions because they cause diseases in the carriers that reduce the chance the mutations will be passed on to future generations.
Scientists know that another mutant version of the hemoglobin gene, which produces abnormally shaped red blood cells known as "sickle cells," provides significant protection against malaria. People who carry two copies of this mutant gene develop a lethal disease called sickle-cell anemia. They rarely live beyond 20 years old.
Two forms of another hemoglobin disorder called thalassemia also confer partial resistance to malaria. Thalassemia is caused by genetic mutations in the hemoglobin genes. Like the sickle cell genes, the thalassemia genes have not spread to all people in malaria-prone areas because the negative effects of the mutations outweigh the resistance to malaria.
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