US researchers have found that a slight difference in a person’s genetic code can determine whether they respond to a round of treatment for hepatitis C infection.

The researchers said that tests looking for this deviation could be used to help determine which patients are more likely to benefit from treatment, and the findings may also explain why some ethnic groups respond much less to treatments than others.

“This discovery enables us to provide valuable information to patients that helps them and their physicians decide what is best for them,” said David Goldstein, a genetic researcher at Duke University in Durham, North Carolina.

Hepatitis C is a liver disease that is transmitted through the blood and can lead to chronic problems such as cirrhosis and liver cancer and may lead to death. More than 170 million people worldwide are infected with the disease.

Typical treatment with interferon in addition to the antiviral ribavirin takes 48 weeks and some patients develop side effects, prompting them to stop treatment, and blacks are less likely to respond to treatment than whites, and no specific reason is known for this.

According to Goldstein’s study, published in the journal Nature, this may be due to a one-letter difference in the genetic code near the interleukin 28b gene, which plays a role in fighting infections.