THURSDAY, Jan. 6, 2005 (HealthDayNews) -- The ability to avoid infection with the AIDS virus depends in part on how many copies of an HIV-fighting gene a person has, a new study says, and the number of those genes varies greatly between and even within racial and ethnic groups.
The study found that people with more copies of the gene were less likely to develop HIV or full-blown AIDS. And while researchers found that black Americans as a whole had more copies than did whites, this didn't mean that whites were more prone to get the virus: Rather, susceptibility was determined more by how many copies people had in relation to others of the same race.
"Individual risk of acquiring HIV and experiencing rapid disease progression is not uniform within populations," Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), said in a statement. The NIAID sponsored the study.
The discovery might someday help in the search for an effective vaccine against AIDS, said Dr. Matthew J. Dolan, director of the Defense Institute for Medical Operations, part of the group reporting the work in the Jan. 7 online issue of the journal Science.
"If we understand the differences in genetic variations, we might be able to generate vaccines with stronger effects," Dolan said.
In addition, better knowledge about individual genetic defenses against HIV "could be used to make decisions about the tailoring therapy for individual persons," he said.
But those hopes lie in the future, Dolan said. "What this [the new study] does is to set the foundation of basic science about HIV infection," he said.
The study is one of many arising from observations that "many people who are exposed to the virus don't get infected," said Dr. Sunil K. Ahuja, professor of medicine and microbiology and immunology at the University of Texas Health Science Center in San Antonio and lead author of the journal report.
The most direct evidence comes from children born to mothers who are HIV-positive, Ahuja said. Only 10 percent to 30 percent of those children become infected, he said, which has led to a search for viral, environmental, and genetic factors that influence the risk of infection.
Earlier genetic research turned up a molecule called CCR5, which sits on the surface of white blood cells. HIV enters the body by attaching itself to CCR5, and "people who don't have CCR5 don't get infected," Ahuja said.
The new study focused on the gene that produces a molecule designated CCL3L1, which acts to block the HIV virus from connecting to CCR5. Ahuja, Dolan, and researchers from more than half a dozen other institutions used blood samples to count the variation in the number of CCL3L1 genes in 4,308 persons, HIV-positive and HIV-negative.
The group included "more than a thousand [U.S.] military people with HIV infection," Dolan said. "All work for the Department of Defense and all have medical benefits, so they constitute a medically balanced group."
Race or ethnicity has a strong effect on the number of CCL3L1 genes, with persons of African descent having a significantly greater number than non-Africans, the researchers found. HIV-negative African-American adults averaged four copies of the gene, while participants of European descent averaged two copies. Hispanic-Americans averaged three copies.
In general, HIV-positive individuals had fewer copies of the gene than HIV-negative persons. Each additional CCL3L1 copy decreased the risk of infection by 4.5 percent to 10.5 percent, with the percentage varying between different racial or ethnic groups.
A lower number of CCL3L1 genes was also associated with faster progression to full-blown AIDS. And the risk of infection and progression was highest for persons with a low number of CCL3LI genes and variants of CCR5 that more readily accepted HIV, the study found.
Genetic testing might someday lead to screening programs to detect individuals at higher risk of HIV infection, Dolan said. "But we hope to get to the point where we understand enough about the genetics of AIDS to get a better fit so we could better tailor therapy."
More information
The U.S. Department of Health and Human Services offers a guide to HIV and AIDS.
