Anti-Malaria Gene Found in Africa, Study Says
Bijal P. Trivedi
National Geographic Today
|November 14, 2001|
One in five people in the African country of Burkina Faso carries a gene
that protects them against malaria, according to a new study.
Understanding how the gene prevents severe malaria could lead to the
development of protective drugs.
Researchers led by David Modiano
of the University of Rome, Italy, have quantified the benefits of
carrying one or two copies of the hemoglobin C gene (HbC). The gene
produces a slightly mutant version of hemoglobin, the protein that
carries oxygen in red blood cells.
Although the scientists do not know how or why it happens, hemoglobin C reduces the chance that a person infected with the parasite that causes malaria, Plasmodium falciparum, will develop clinical symptoms and get sick.
The study found that in Burkina Faso, nearly 22 percent of the population carries one copy of the HbC gene. These people are 29 percent less likely to become sick with malaria after they have been infected, compared with people who carry the more common form of the gene, hemoglobin A.
People with two copies of HbCone copy inherited from each parentreceive almost complete protection from the disease. They are 93 percent less likely to develop symptoms.
The findings are of wide interest because malaria is the world's most devastating parasitic disease. More than 300 million new cases occur worldwide each year, resulting in about one million deaths, according to a spokesperson at the World Health Organization, based in Geneva, Switzerland.
More than 90 percent of all deaths from malaria occur in sub-Saharan Africa.
In the Burkina Faso study, Modiano's team studied 3,513 healthy subjects and 835 malaria patients at Ouagadougou University Hospital. The researchers first analyzed each patient to determine what versions of the hemoglobin gene they carried. Of the 359 patients found to have two copies of the protective gene, only one had severe malaria.
The results are published in the November 15 issue of the journal Nature.
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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