Around 40,000 new HIV infections occur each year in the United States. However, a specific gene mutation present in about 10 percent of Caucasians may make them resistant to infection by HIV-1, with about one percent having almost full immunity.

Researchers have found resistance and high levels of immunity only against the HIV-1 strain. HIV-1 is the most prevalent type of HIV infection in the Western world. The HIV-2 strain was discovered in 1986 and mostly infects people in West Africa.

The mutation is in the gene for receptor CCR5, a protein on the surface of immune cells which the HIV virus binds to. In this mutation, there is a deletion of the 32nd base pair. This means that this gene consists of multiple base pairs and in some people the 32nd base pair is not present.

CD4 cells, which are white blood cells that help protect the body from foreign pathogens, contain the CCR5 receptor and are the main cells that are targeted during HIV infection. However, this mutation eliminates CCR5 expression on the surface of the cell, preventing HIV from binding to it.

This mutation appears to offer almost full immunity to those who inherit two copies of the gene mutation, one from each parent. Those who possess two copies are known as homozygous for the mutation. This accounts for about one percent of Caucasians.

Those who only inherit the mutation from one parent appear to have a higher resistance to infection and may even have slower disease progression in the case of infection. Those who possess one copy are known as heterozygous for the mutation. This occurs in about 10 percent of Caucasians.

This mutation is found in two to five percent of Middle Easterners and those of Indian decent. However, it has not been found in any African or Asian populations.

Several theories have been discussed as to why those of European descent seem to possess this mutation over other heritages.

One possible explanation is that this mutation occurred around the time of the Black Death in Europe. According to the Public Broadcasting Service, the areas hit hardest by the Black Plague match those where the gene for HIV resistance is the most common today.

Individuals who inherited the mutation from both parents still need to use caution to prevent HIV infection. The presence of a homozygous CCR5 mutation does not guarantee 100 percent immunity.

According to a study published in 2002 in The Lancet, there have been rare cases where HIV infection has occurred in those homozygous for the mutation.

Therefore, safe-sex practices still must be used when an HIV-negative individual is engaging in sexual activity or other high-risk activities with an individual who has the homozygous CCR5 mutation.

A 2001 study published in the Journal of Acquired Immune Deficiency Syndrome analyzed the prevalence and rate of infection for those homozygous and heterozygous in the CCR5 mutation.

Researchers observed that men who were heterozygous for the mutation had a 70 percent reduced risk of infection compared to those without the mutation.

A February 2009 study published in the New England Journal of Medicine analyzed the effects of transplanting the homozygous CCR5 mutation into a 40-year-old man. After receiving a stem-cell transplant from a CCR5 homozygous mutation donor, a procedure done to treat his leukemia, the man was able to discontinue HAART medication. HAART is typically composed of three or four antiretroviral drugs in combination.

Twenty months after discontinuation, his viral load, which is the amount of HIV in the blood, was still undetectable.

This phenomenon is not a new discovery, but new research on this topic is always occurring. In 1995, a researcher at the Institute of Human Virology at the University of Maryland School of Medicine, discovered that chemokines, or proteins secreted by cells in the immune system, blocked HIV-1 in a test tube experiment.

The CCR5 mutation’s effects have been studied in relation to other illnesses such as smallpox and multiple sclerosis.

However, studies have also been conducted potentially linking the presence of this mutation to an increased risk for the acquisition of West Nile Virus and Hepatitis C.

Testing for this mutation appears to be mostly research based. It is performed at only select laboratories. Ask your physician for more information on gene testing.

For more information on the study analyzing CCR5 implantation, visit the New England Journal of Medicine.