Mutations in the core promoter and precore regions are frequently found in hepatitis B e antigen (HBeAg)-negative patients, but precore stop codon mutation is restricted to hepatitis B virus (HBV) genotypes that have T at nucleotide 1858. The aims of this study were to determine the role of core promoter and/or precore mutations in HBeAg seroconversion and their impact on the subsequent course of liver disease, and to determine if core promoter mutations are more frequently selected in patients with HBV genotypes that preclude the development of precore stop codon mutation. Serial sera from 45 patients with chronic HBV infection were polymerase chain reaction (PCR)-amplified, and the HBV core promoter and precore regions were sequenced. Ninety-two percent of patients had core promoter or precore mutations after HBeAg seroconversion: 42% had core promoter changes only, 38% had precore stop codon mutations only, and 12% had changes in both regions. Seventy-three percent of the patients had persistently normal aminotransferases, and only 8% had multiple flares in aminotransferases after HBeAg seroconversion. Core promoter changes were significantly more common in patients infected with HBV who have C at nucleotide 1858 (91% vs. 27%; P F .01), while precore stop codon changes were exclusively found in patients infected with HBV who have T at nucleotide 1858 (87% vs. 0; P F .01). The vast majority of our patients had core promoter and/or precore mutations after HBeAg seroconversion. Nevertheless, most patients had sustained remission of liver disease. Our data suggest that core promoter changes are preferentially selected in patients infected with HBV genotypes that pre-clude the development of precore stop codon mutation. (HEPATOLOGY 1999;29:976-984.)
Mutations in the precore region of the hepatitis B virus (HBV) genome have been reported in many hepatitis B e antigen (HBeAg)-negative patients with chronic HBV infection. The predominant mutation involves a G-to-A change at nucleotide 1896 (A1896), which creates a premature stop codon at codon 28 (Fig. ). This mutation prevents the translation of the precore protein and completely abolishes the production of HBeAg. Longitudinal studies found that A1896 emerges or is selected around the time of HBeAg seroconversion. These findings suggest that A1896 plays an important role in HBeAg clearance. However, not all patients develop A1896 after HBeAg seroconversion; some patients retain wild-type precore sequence, while others have undetectable HBV DNA in serum (by polymerase chain reaction [PCR] assay). It is now recognized that the occurrence of A1896 is restricted to HBV genotypes with T at nucleotide 1858. A change from G to A at nucleotide 1896 increases the stability of the stem-loop structure of the pregenome encapsidation sequence (β) when the opposite nucleotide at 1858 is a T (T1858), but this change disrupts a pre-existing C-G pair when the nucleotide at 1858 is a C (C1858). The restriction of A1896 to specific HBV genotypes accounts for its high prevalence in Asia and the Mediterranean basin, where the predominant HBV genotypes (B, C, and D) frequently have T1858, and its low prevalence in North America and Europe, where the predominant HBV genotype (A) almost always has C1858. In our previous studies of Chinese patients from Hong Kong, we found that only 60% of patients were infected with HBV genotypes that have T1858. Nevertheless, patients infected with HBV genotypes that have C1858, which precludes the development of A1896, appeared to clear HBeAg at rates similar to those infected with HBV genotypes that have T1858. Recent studies reported that mutations in the core promoter region can be found in many HBeAg-negative patients; the most common mutations involve a two-nucleotide substitution: A-T at nucleotide 1762 and G-A at nucleotide 1764 (TA) (Fig. ). In some patients, the TA changes were not associated with A1896, suggesting that mutations in the core promoter region alone may play a role in HBeAg clearance. This hypothesis is supported by in vitro observations that the TA changes decrease transcription of precore mRNA and secretion of HBeAg. However, TA changes have also been