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One Disease Deciphers Another

Since British geneticist Anthony Allison found that individuals with a mutated copy of the sickle cell anemia gene are protected from malaria 67 years ago, researchers have wondered about the relationship between the two diseases, says Nature News' Meredith Wadman. Now, thanks to a new paper in Science, they have an answer. Researchers at Heidelberg University compared healthy red blood cells to cells infected with the malaria parasite Plasmodium falciparum and with cells from sickle cell patients. The sickle cell blood came from people carrying the mutated S gene that causes the disease "as well as another mutation, dubbed C, which occurs at the same spot," Wadman says. "Both mutations lead to the substitution of a single amino acid in the hemoglobin molecule, causing the hemoglobin to aggregate abnormally inside the cell."

In healthy red blood cells, short pieces of actin filament are clustered under the cell membrane, and the researchers observed that the malaria parasite uses the actin to transport the parasite's protein to the cell surface, making the cell "sticky" — a hallmark of the disease. In sickle cell blood, however, the researchers "observed that the hijacking of actin filaments by the parasite was hobbled," Wadman says. "The actin bridge was cut off from the intracellular depot of adhesin, and the vesicles that would normally transport the adhesin to the cell surface were floating free in the cytoplasm." The researchers say that evolutionary pressures may have led to the development of the sickle cell gene mutation in order to protect people from malaria, by preventing it from using the blood cells' actin. People who carry one copy of the gene mutation still make enough normal hemoglobin to be asymptomatic for sickle cell anemia, Wadman says, adding that "being a carrier confers a survival advantage in countries where malaria is endemic."

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