Japanese scientists on Monday said they had uncovered a genetic variant that could help explain why Asians seem especially vulnerable to the hepatitis B virus (HBV).
Prevalence of HBV varies greatly around the world, from as high as five to 12 percent in China and Thailand, to just 0.2 to 0.5 percent in North America and Europe.
Some people who are infected with the virus suppress it spontaneously after a mild illness, but others develop a serious long-term infection.
Of those who are chronically infected, between two or 10 percent eventually develop liver cirrhosis, which in turn can lead to liver failure or liver cancer.
Why some individuals eliminate the virus and others fail has been an area of big debate.
The age at which infection occurred, sex, chronic alcohol abuse and co-infection with other hepatitis virus are among the factors that influence the outcome, but scientific interest is also focussing more and more on genetic background.
In a study published online in the journal Nature Genetics, University of Tokyo researcher Yusuke Nakamura and colleagues pored over the genomes of 786 Japanese with chronic hepatitis B infection, and compared the result with another dataset, this time from 1,300 cases of infected Japanese and Thais.
Patients that had variants in two immune-system genes, HLA-DPA1 and HLA-DPB1, were more than 50 percent likelier to become chronically infected with HBV compared with healthy controls.
Finding out the molecular role of these two variants could shed light on how the virus gains a foothold and opens up new paths for drugs, the paper says.
More than 400 million people around the world are chronically infected with HBV, according to a 2003 estimate quoted in the study.
HBV is contracted mainly via contact with infected blood and semen or from an infected mother to her newborn.