Study: Why Whites Are Less Susceptible to AIDS

A team of New York researchers may have found an explanation for why, in the United States and Europe, heterosexual transmission of HIV is rare among whites, but more common among Asians and people of African descent.

Dr. Harold Burger, of the New York State Wadsworth Laboratory in Albany, and his team found a statistically very significant set of genetic differences between HIV-positive and HIV-negative American women. Their study focused upon 2,047 HIV- positive women, compared with a pool of 558 race- and age-matched HIV-negative women. It isolated a genetic mutation that had previously been shown in men to be protective against HIV infection.

The mutant gene, called delta-32, if inherited from both parents, results in an abnormal, and in this case protective, receptor called ccR5 on the surface of the subject's cells. Because HIV cannot recognize the mutant delta-32 form, it cannot infect the cell. Some individuals inherit the gene from one parent and can be infected with HIV, but some studies in men have indicated that they are less likely to rapidly develop the lethal disease after infection.

The Burger study is the first to examine a large pool of women for the mutation and to compare the women by race. Overall, the study found that all HIV-negative women were about twice as likely to have the protective delta-32 gene than were infected women. "This is almost a no-brainer," Burger said. "This gene in heterozygous form [from one parent] confers partial protection against HIV. So if you've got it, you're partially protected. If you're in a population group that doesn't have that protection, you're at greater risk."

White women carry the heterozygous form of delta-32 far more frequently than any other women. About 1.2 percent of all white women who are HIV-negative carry the mutant gene. Only 0.6 percent of HIV-infected white women carry the gene. However, only 0.2 percent of HIV-negative African-American women carry the delta-32 gene. Among those who are HIV-positive, the frequency of delta-32 is only 0.1 percent.

"This supports mathematical predictions that having a low frequency of delta-32 in non-Caucasians may render those populations vulnerable to far greater and more explicit HIV epidemics," Burger said in a presentation on Wednesday at the Ninth Conference on Retroviruses and Opportunistic Infections. "And it may explain, in part, the rapid epidemics we see unfolding in Asia and Africa."

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