A slight genetic variation may explain why some people are less likely to respond to a treatment for hepatitis C infection, researchers say.

The study of 1,137 people in the U.S. and Europe with a chronic hepatitis C infection suggested standard treatment wiped out the virus among 80 per cent of study participants with a genetic variant but only 30 per cent among those who lacked it.

"This discovery enables us to give patients valuable information that will help them and their doctors decide what is best for them," genetics researcher David Goldstein, of Duke University in Durham, N.C., said in a statement.

In Sunday's online issue of the journal Nature, Goldstein and his colleagues said African-Americans who had the gene variant showed a better response than whites who didn't have it, which shows the gene is a better predictor than ethnicity.

The variant explains about half of the difference in response rates between African-Americans and those of European ancestry, researchers said.

The variant is found near the Interleukin-28B or IL28B gene, which plays a role in fighting off infections, the team reported.

Treatment for chronic hepatitis C may involve 48 weeks of interferon and the antiviral drug ribavirin.

Since the potential side effects can be severe, the researchers said testing for the variant may help guide patients and doctors in deciding when to start or postpone treatment. The drug combination is effective in about 30 to 50 per cent of patients, according to the World Health Organization.

An estimated 242,500 Canadians are infected with hepatitis C, according to the Public Health Agency of Canada. The blood-borne liver disease causes inflammation of the liver, and in some cases, can lead to severe damage or cancer in the organ. It affects an estimated 170 million people worldwide, the WHO said.

The hepatitis C virus is spread through contact with infected blood, such as sharing poorly sterilized needles or other contaminated equipment.

The study was funded by Schering-Plough, which makes one of the standard hepatitis C treatments.

With files from The Associated Press