By Will Dunham
WASHINGTON, July 16 A gene variant that emerged thousands of years ago to protect Africans from malaria may raise their vulnerability to HIV infection but help them live longer once infected, researchers said on Wednesday.
The findings could help explain why AIDS has hit Africa harder than all other parts of the world.
People with the version of the gene have a 40 percent higher risk of becoming infected with the human immunodeficiency virus, or HIV, researchers in the United States and Britain wrote in the journal Cell Host & Microbe.
In Africa, the gene variant may account for 11 percent of HIV infections, the researchers said.
Sexual behavior and other social factors cannot completely explain why more than two-thirds of the world's 33 million people infected with HIV live in sub-Saharan Africa, the researchers said. So genes may be playing a pivotal role.
The gene in question controls a protein on the surface of red blood cells.
But even as it elevates a person's susceptibility to HIV infection, having this version of the gene seems to slow the progression of AIDS. Those with the variant who have been infected with HIV live roughly two years longer than people who do not have it, the researchers said.
Having the variant has become "a double-edged sword," said researcher Sunil Ahuja of the University of Texas Health Science Center at San Antonio.
About 90 percent of people in sub-Saharan Africa have this gene variant, and about 60 percent of Americans of African descent also possess it, according to the researchers.
Of the 2.1 million people who died of AIDS worldwide last year, 1.6 million were from sub-Saharan Africa, according to the United Nations.
VARIANT FROM LONG AGO
The protein linked to the gene is called Duffy Antigen Receptor for Chemokines, or DARC. People with the variant do not have this particular receptor -- a type of molecular doorway into cells -- on their red blood cells.
People lacking the receptor are protected against infection by a malaria parasite known as Plasmodium vivax. This parasite is not the one responsible for the multitudes of malaria deaths that now occur yearly in Africa, but is still seen in some parts of Asia and the Middle East.
The researchers believe the gene variant arose long ago, perhaps protecting people in Africa against a deadly strain of malaria that may have swept through populations.
"We're probably talking about tens of thousands of years ago," said Robin Weiss of University College London.
The researchers made their findings in black Americans, not in a population in Africa. They looked at 1,266 HIV-infected people in the U.S. Air Force who were tracked since the 1980s, as well as 2,000 noninfected people.
They found the variant to be far more common among the U.S. blacks infected with HIV than those not infected.
Only a small proportion of people not of African descent carry this genetic mutation, and it is just about absent in people of European descent, the researchers said. (Editing by Maggie Fox and Xavier Briand)