More than 170 million people worldwide have been infected with the Hepatitis C virus that can cause liver failure, cancer, and death. There is no known cure, but about 20 percent of the people who contract the disease fight it off without treatment. Researchers from Great Britain and the United States recently looked at the genetic makeup of people who had hepatitis C to try to find out what was different about the 20 percent who got better on their own.

What the researchers wanted to know: Why does hepatitis C affect some people permanently and not others?

What they did: The researchers looked at the gene structure of 685 people who had hepatitis C and 352 people who had been diagnosed with the disease but whose bodies had gotten rid of the infection. They studied the particular pattern of how genes on different chromosomes interacted with each other and activated specific cells in different people.

What they found: The researchers found that people who had beaten hepatitis C had a different genetic makeup from others whose bodies could not get rid of it. Everyone has certain types of immune cells called natural killer cells, which act as the emergency response team for the immune system, rushing to the site of a new infection. Some people's genes line up in such a way that they are less effective at inhibiting these natural killer cells, meaning that the cells are more often activated. That variation seems to work in their favor in the case of hepatitis C because the natural killer cells respond quicker and more aggressively to the infection.

What it means to you: Hepatitis C still has no cure, and this finding is only a small step toward that goal. However, knowing why the infection is killed in some people but not in others could give doctors a direction for further research into therapies that might help the 80 percent whose genes are not configured to deal with the infection.

Caveats: Hepatitis C is usually contracted through blood, such as a blood transfusion or sharing needles. For people who had contracted the disease in a way where the virus arrived en masse, as in a transfusion, even the winning combination of genes was no match for the hepatitis C virus. Only those who had been exposed to a small amount of blood and had the right genetic lineup were able to rid their bodies of the infection.

Find out more: A basic fact sheet about hepatitis C, including symptoms and prevention, is on the Centers for Disease Control and Prevention website. A much more detailed explanation about the disease, as well as all other types of hepatitis, can be found at www.epidemic.org a site developed by the C. Everett Koop Foundation at Dartmouth College and hosted by Koop, the former U.S. surgeon general.

Read the article: Khakoo, S.I. et al. "HLA and NK Cell Inhibitory Receptor Genes in Resolving Hepatitis C Virus Infection." Science. Aug. 6, 2004. Vol. 305, pp. 872–874.

Abstract online: www.sciencemag.org