Different mutation rates in the basal core promoter and precore regions between hepatitis B virus subgenotype F1b clusters.

Hepatitis B virus (HBV) is the main etiological agent of hepatocellular carcinoma (HCC) worldwide. It has been classified into nine genotypes and several subgenotypes, with uneven global distribution. There is growing evidence that the viral genotype influences the course and outcome of chronic hepatitis B infection. Two evolutionarily different clusters of the subgenotype F1b, called basal and cosmopolitan, have been described. The two clusters have constrained geographical distribution, with the particular feature that the basal cluster is present in regions of high HCC incidence, while the Cosmopolitan cluster is found in regions of low HCC incidence. The BCP/pC region was sequenced in 68 cases chronically infected with the F1b subgenotype to determine if there was a differential pattern of pathogenic-associated mutations between both clusters. Twenty-two of the 68 cases belonged to the subgenotype F1b basal cluster and 46 to the cosmopolitan cluster. Among the HBeAg-negative patients the A1762T/G1764A and G1896A mutations were more frequently found in the basal samples (85.7 and 92.9%) compared to the cosmopolitan ones (50 and 18.2%). Interestingly, no HBeAg loss-associated mutations were observed in 7.1 and 36.4% of the basal and cosmopolitan cases, respectively. The different rate of mutations associated with a more severe course of chronic hepatitis in the basal cluster would support the difference in the HCC incidence rate in the geographical regions where the basal cluster is restricted.