Selected to survive. Many people in Southeast Asia - including the Karen - have a mutation that provides some protection against Plasmodium vivax .
Gertha / Wikimedia
A mutation common in Southeast Asia which causes anemia also provides some protection against malaria, according to a new study. The mutation does not protect carriers from the most known cause and the most severe disease, but from a more benign parasite that has been studied much less.
Scientists already know that humans long battle with malaria has shaped our genome. One third of sub-Saharan Africans, for example, carry a mutation that causes sickle cell anemia, but also protects against malaria: The deformed red blood cells prevent the malaria parasite from entering. The researchers identified other mutations as well, but almost all protect against Plasmodium falciparum , a parasite transmitted by anopheles mosquitoes that kills more than a million people each year.
In the current study, geneticist Anavaj Sakuntabhai of the Institut Pasteur in Paris and colleagues examined a mutation in the gene encoding the enzyme glucose-6-phosphate (G6PD), an enzyme that helps protect cells against damage by oxidation of molecules. Mutations in G6PD can cause jaundice in newborns, anemia after infection with certain pathogens, and other problems. Some of these mutations are very common in some areas, including parts of Asia and Africa. Thus, researchers have long suspected that they must have a positive side - perhaps a protection against malaria, as G6PD is important in red blood cells. But studies on P. falciparum in Africa has not found a solid link.
group Sakuntabhai instead turned his attention to Thailand, where P. falciparum and its lesser known cousin, P. vivax , cause malaria. The team zoomed in on a mutation called G6PD Mahidol - after the father of the current King of Thailand, a famous physician and advocate of public health - which occurs throughout Southeast Asia and is the most common Myanmar. Sakuntabhai and colleagues first undertook a genetic study among 384 people - most of them belonging to an ethnic group called Karen - in Suan Phung district of Thailand, where malaria is prevalent. The frequency of mutation Mahidol was 24%, and using a so-called long range haplotype test - a technique that helps to sniff the recent natural selection in the genome - the team found that natural selection has indeed strongly favored transfer, from there about 1500 years. Scientists believe that malaria spread along human agriculture, creating small pools of standing water that mosquitoes like. As it happens, researchers think the Karen moved out of Tibet and began growing rice there are about 1500 years, said Sakuntabhai.
In clinical studies, the team showed that the mutation Mahidol really makes a difference. During a period of 7 years, those with the mutation had roughly the same number of malaria episodes as noncarriers, the authors report in today's issue of Science, but the mutation reduced the number of P. vivax in their blood. Women who had one copy of the gene were 30% less noise; those with two copies had 61% less. Because G6PD is on the X chromosome, men can get a copy at most; who had 40% less noise than controls did. "The parasite is not happy at all, it can not grow as well," said Sakuntabhai. But Mahidol had no effect on P. falciparum numbers.
P. vivax "is generally dismissed as an insignificant actor" who form the human genome as P. falciparum did, said Richard Carter, a geneticist malaria at the University of Edinburgh in the UK. the new study shows that it is probably wrong. P. vivax is not a fast killer as P. falciparum, and today most people can buy medicine to treat it. But in the past, people may have suffered from repeated and long periods with P. vivax , Carter said that "slowly grind down." Reductions in parasite density seen in Mahidol carriers may have lengthened the life of carriers considerably and allowed them to have more children.
Sakuntabhai adds that even today P. vivax may be a bigger health problem than people assume. A study published last year in PloS Medicine showed that P. vivax Children killed in Papua New Guinea, not yet reported by another group that saw Sakuntabhai shows that the parasite can cause anemia over a month after the infection is completed. . "The bottom line is, we should not underestimate P vivax ," he said -. "And we should study more"
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