Gene Means African AIDS Progression May Slow

By Merritt McKinney

Over the next 100 years, more and more people living in sub-Saharan Africa will carry a genetic mutation that will prolong the time between infection with HIV (news - web sites) and the development of AIDS (news - web sites), California researchers predict.

The genetic mutation will become more common as an unfortunate result of natural selection as the AIDS epidemic ravages the continent, they explain.

In 1999, 20% or more of adults in several sub-Saharan nations including South Africa, Botswana, Zimbabwe and Zambia, were infected with HIV. Assuming that the current rate of HIV infections and AIDS deaths do not change, the lifetime risk of dying from AIDS for a boy who was 15 years old in 1999 is 65% in South Africa and nearly 90% in Botswana, according to Dr. Paul Schliekelman and colleagues at the University of California, Berkeley.

But mutations in an immune system receptor can influence a person’s risk of getting HIV or of developing AIDS after being infected. Known as CCR5, this "co-receptor’’ is one of two receptors on immune system cells that HIV needs to gain access to cells.

People who have two copies of a mutant form of the CCR5 gene—one from each parent—have a much lower risk of being infected with HIV than people who do not have the mutations. Having a single copy of the gene does not protect a person from being infected with HIV, but it does slow down the progression to AIDS.

The CCR5 mutations most common in Africa delay the progression of AIDS by 2 to 4 years, Schliekelman’s team reports in the May 31st issue of the journal Nature. Based on the assumption that people with AIDS-delaying mutations will stay healthier longer during their prime reproductive years, Schliekelman and his colleagues predict that more and more African children will be born with a protective form of CCR5.

In contrast, the researchers expect that fewer children will be born with a CCR5 mutation that speeds the development of AIDS, since adults with the mutation are likely to become sicker sooner and to have fewer children.

"The very high prevalence rates of HIV/AIDS in southern Africa are causing natural selection to occur for genetic mutations that delay the onset of AIDS by 2 to 4 years during peak fertility years,’’ one of the authors of the study, Dr. Chad Garner, told Reuters Health.

The researchers predict that 100 years from now, a little more than half of Africans will have a CCR5 mutation that delays the progression of AIDS. According to their estimates, the average time between infection with HIV and development of AIDS should increase about a year.

SOURCE : Nature 2001 ;411:545-546.