Analysis Of Genetic Mutation Of HBV Precore/basal Core Promoter In Patients With Chronic Severe Hepatitis B

The outcome of hepatitis B virus (HBV) infection depends on the interplay between the virus, the hepatocyte, and the host's immune response. HBV-related severe hepatitis carries a high mortality rate and is an important cause of death among infectious diseases in China. The pathogenesis of chronic severe hepatitis B (CSHB) is not fully understood right now. Various genetic mutations have been considered as the basic factor influencing HBV biological features. Evidence has been accumulating that certain HBV mutants may change the ability of replication of the virus, alter HBV antigen epitope which is related to either an exaggerated host immune response or evasion of the virus from immune survailance, and lead to either resistance to antiviral agents. Thus, HBV mutation is assocated with the persistent infection or the severe damage of hepatocytes. HBV genome contains four open reading frames (ORF) consist of S-ORF (pre-S1, S2, S regions), C-ORF (precore and C regions), P-ORF, and X-ORF. In addition, several gene fragments with replication/transcription modulatory activities are also included in HBV genome. Some studies have analyzed the significance of HBV genetic mutation with fulminant hepatitis B occurrence, including the analysis of precore/basal core promoter (BCP) region. Some mutations in this region have been proved to abrogate HBeAg expression/secretion or increase viral replication. It is suggested that secretary HBeAg will alleviate injury of HBcAg-expressing hepatocytes by cytotoxic T cells (CTL), for HBeAg and HBeAg share CTL immunological epitopes. Therefore, precore/BCP mutations may have negative effect on immunotolerance and thus associate with aggravation of chronic hepatitis B. However, the results of precore/BCP mutation investigation are discrepant with controversial opinions on the mutation significancy, possibly due to relative small sampling and difference in methodology. Further studies are needed to address this issue. In this study, we investigated the association of HBV precore/BCP mutation with the occurrence of CSHB.Abstract Objective To analyze the characterization and significance of genetic mutation of HBV precore/BCP in patients with CSHB. Methods Sera from 87 patients with CSHB and 196 patients with chronic hepatitis B (CHB) were collected for extraction of HBV DNA. The precore/BCP gene fragment was amplified by nested PCR and analyzed by direct DNA sequencing. The data were processed by NBI software. Substitutions at G1896, G1862, G1899, A1762, G1764 and T1753 were specially focused on. Results Only 3.4% of CSHB patients were mutation-negative at all 6 sites, markedly lower than CHB patients (28.1%, P < 0.01). At five of the 6 sites, the increase of mutation occurrence was statistically significant in CSHB patients compared with CHB patients. CSHB patients had a remarkable increase of multiple-site or insert/deletion mutations, with 56.3% vs. 35.2% (P<0.01) for >three-site substitution, 25.3% vs. 8.7% (P < 0.01) for >four-site substitution, and 10.3% vs. 1.0% (P <0.01) for insertion/deletion. Conclusion Mutation accumulation in HBV precore/BCP regions is associated with CSHB. Screening the mutations combined with clinical data analysis is valuable for understanding the pathogenesis of CSHB.