In an attempt to find an explanation for the high frequency of AIDS cases within the world’s black populations, an international team of researchers discovered that blacks present a gene variant, which, while ensuring a higher level of protection against some types of malaria, increases the vulnerability to HIV infection.

About three quarters of the 33 million people worldwide who are currently infected with HIV live in Africa south of the Sahara, where most people are black.

For the study, study co-author Dr. Sunil K. Ahuja, a professor at the University of Texas Health Science Center in San Antonio and colleagues studied how genetics affects AIDS in more than 1,200 members of the US military who became infected with HIV.

The researchers concentrated on a specific gene, called Duffy Antigen Receptor for Chemokines (DARC gene), which is nonexistent in whites, but is held by approximately 90 percent of Africans, meaning that it may be responsible for an estimated 11 percent of the HIV burden here. The same gene is also held by 60 percent of African-Americans.

This gene influences the levels of chemicals called chemokines, which defend the body against viruses.

After putting aside social and economic differences, which might have led to HIV infections, the researchers discovered that people with the genetic variant were 40 percent more likely to be susceptible to the illness.

“There are many social issues, such as poverty and lack of access to health care, that contribute heavily to the risk of HIV. If you take care of those, you can go a long way toward reducing the risk of HIV,” Dr. Ahuja said.

“In sub-Saharan Africa, the vast majority of people do not express DARC on their red blood cells and previous research has shown that this variation seems to have evolved to protect against a particular form of malaria. However, this protective effect actually leaves those with the variation more susceptible to HIV,” Professor Robin Weiss, UCL Infection and Immunity who co-authored and supported the study, said.

On the other hand, people with the gene variant live an average of two years longer with the disease once they get it, the study found.

“It turns out that having this variation is a double-edged sword. The finding is another valuable piece in the puzzle of HIV-AIDS genetics.”

The study was published in the July 17 edition of Cell Host & Microbe.