Hepatitis B virus precore mutants are identical in carriers from various ethnic origins and are associated with a range of liver disease severity

Method for detection of epsilon-secondary structure in the precore region of human hepatitis B virus DNA using a fluorescence-based polymerase chain reaction-single-strand-conformation polymorphism technique with capillary electrophoresis

A portion of the precore region of the human hepatitis B virus (HBV) genome is the signal sequence with an epsilon secondary structure, which plays a role in the encapsidation of HBV pregenome RNA. To determine the genetic mutations which occur in the precore region of HBV, we have devised a typing method using a fluorescence-based polymerase-chain-reaction-single-strand conformation polymorphism technique with automated capillary electrophoresis (CE-FSSCP). Using the cloning sequencing method, we analyzed serum samples from 10 patients with hepatitis B, and detected three types of HBV-DNA including two mutants which are crucial to the function of the encapsidation sequence: position 1896 G (guanine) to A (adenine, stop codon), position 1899 G to A, and wild-type. We performed CE-FSSCP analysis of these three types of HBV-DNA and described conditions for determination of the mutations which play roles in the encapsidation of the HBV pregenome. The two types of epsilon mutants and wild-type DNA were identified as separate individual peaks respectively. The observed migration times of the three types of DNAs agreed fairly well with estimates obtained from total RNA secondary structure energy.

Emergence and selection of HBV variants in an anti-HBe positive patient persistently infected with quasi-species

BACKGROUND/AIMS

Infection with the hepatitis B e antigen (HBeAg) negative variant of hepatitis B virus (HBV) causes chronic liver disease characterised by occasional acute exacerbations. This virus exhibits a high prevalence of mutations in the core region. Our aim was to study the changes in the pre-core/core region of the virus in relation to exacerbations of the disease.

METHODS/RESULTS

We performed direct sequencing on DNA amplified from 7 sequential sera taken over a 5-year period from a hepatitis B surface antigen (HBsAg) and anti-HBe positive Greek patient infected with the HBeAg negative variant. The patient had chronic hepatitis with several acute exacerbation episodes and underwent interferon therapy twice. We found significant variability in the core region at different time points. To determine whether these variants were present in the initial serum sample and subsequently selected under immune pressure or whether they arose de novo during the course of the disease, we cloned the pre-core/core region from 4 sera before and after episodes of acute exacerbation. Fifteen clones from each time point were sequenced. Fourteen nucleotide mutations in the pre-core/core region were recorded, 7 (50%) of which led to amino-acid substitutions. All the amino-acid changes occurred at recognised B- and CD4+ epitopes. The cloning results indicate the presence of quasi-species in all the samples investigated. Some of the variants present as a minor population in the first sample appear to have been selected and become dominant in subsequent sera. However, the emergence of novel variants, not present at a detectable level in earlier samples, during the course of the disease, was also established. The quasi-species nature of HBV only became apparent after the cloning experiments and was not obvious from the direct sequencing results.

CONCLUSIONS

New dominant variants occurring during the course of the disease arose either by the selection of pre-existing mutants that were not detected by direct sequencing or by mutation of existing strains. All changes were located within B- and CD4+ epitopes. The continuous production and selection of variants may enable virus to evade elimination by the immune system, resulting in persistent infection.

Frequency of hepatitis B virus e-minus mutants varies among patients from different areas of China

Four hundred forty-six serum samples from HBsAg-positive chronic hepatitis B patients were collected from five areas in China (eastern coastal city, Shanghai; southwestern inland city, Chengdu; mid-inland city, Wuhan; southern island city, Haikou; and northeastern city, Changchun). Precore stop codon variants (e-minus mutants) were screened using a rapid method of polymerase chain reaction (PCR) amplification of a precore and partial core gene fragment (nucleotides 1785-2172), followed by dot-blot hybridization with specific oligonucleotide probes (M0, and M1 + M2). The sequence of the M0 probe covered the distal precore region of wild-type virus (nucleotides 1887-1908), and the sequences of the M1 and M2 probes were from sequences mutated at nt. 1898, (TGG-->TAG) with or without additional change at nt. 1901. A significantly lower incidence of the precore stop codon was found in anti-HBe-positive serum samples from Haikou (17.6%), whereas in other areas the percentages of this mutation in anti-HBe positive sera ranged from 47.4% to 78.9%. In HBeAg-positive samples, the rate of e-minus mutant in coexistence with wild-type virus was low in specimens from Haikou (9.5%) and Changchun (2.9%) compared to other areas in China. In contrast, coexistence of mutant and wild-type virus was frequently detected in samples from Wuhan (50.0%).

Pathogenesis of chronic liver disease in patients with chronic hepatitis B virus infection without serum HBeAg

Chronic hepatitis B in patients lacking hepatitis B e antigen has been attributed to a hepatitis B virus variant (G-to-A mutation at nucleotide 1896 in the precore region of the genome). We therefore assessed the frequency and significance of this variant among 43 United States patients (10 with chronic hepatitis B seropositive for e antigen, 19 seronegative for e antigen, and 14 healthy carriers). Sera were tested for HBV DNA by polymerase chain reaction and branched DNA assay. The A1896 variant was detected by direct sequencing and ligase chain reaction. Serum HBV DNA was more frequently found among patients with e antigen-positive than e antigen-negative chronic hepatitis B. Viral titers were generally higher in those with e antigen. None of the e antigen-positive and only 24% of e antigen-negative patients harbored the A1896 variant. Patients infected with the variant were more often Asian, had had hepatitis B for longer and had higher levels of viral DNA than HBeAg-negative patients with the wild-type virus. The A1896 variant was found exclusively in patients infected with HBV genotypes C and D. Thus, the A1896 variant is uncommon in the United States. The activity of liver disease appears to be more closely related to the level of HBV replication than the presence of mutations at nucleotide 1896 in the genome.

Hepatitis B

Hepatitis B remains a major public health problem around the world. The discovery of the hepatitis C virus has diverted interest from hepatitis B to this new virus and the epidemic associated with it, but hepatitis B remains a significant pathogen for millions of people worldwide. The World Health Organization has suggested that universal vaccination of children against hepatitis B should be implemented in an attempt to reduce the enormous morbidity and mortality associated with infection of this virus group. The review seeks to identify all the newer discoveries relating to hepatitis B that have been made in the past decade. Reference is made to the appearance of hepatitis B mutants which are able to infect patients previously infected with the wild strain of the virus. The implications of mutants on vaccination programmes is raised, as are issues relating to treatment of hepatitis B infection.

Anti-HBe titre in patients infected with wild-type and e-minus variant of hepatitis B virus

Serum samples from 77 HBsAg- and anti-HBe-positive chronic hepatitis B patients were studied for a G to A point mutation at the 1896 nucleotide of the precore region by polymerase chain reaction and oligonucleotide hybridization. Patients were grouped as: A, infected only by the wild-type virus; B, infected only by e-minus variant; C, coinfected by the wild-type and e-minus variant; and D, no precore/core gene of hepatitis B virus detected. All samples were assayed for the titre of anti-HBe by ELISA and compared as grouped. A significantly higher titre was found in the coinfected group C compared to groups A (p < 0.01) and D (p < 0.05). Results indicate that a high titre of anti-HBe is required as immune selective pressure for E-minus variant to overtake the wild-type virus.

Progress towards the comprehensive control of hepatitis B in Africa: a view from South Africa

The carrier rate of hepatitis B virus (HBV) in black Africans averages 10.4% throughout the continent. Even within each country, however, there may be wide variations. HBV carriage in black Africans is largely established in early childhood, mostly through horizontal transmission. Perinatal transmission also occurs but to a much lesser extent than in the Far East. For unknown reasons, HBeAg positivity rates are much lower in black Africans of childbearing age than in women in the Far East. Universal HBV vaccination of infants in South Africa started in April 1995. Effective integration into the Expanded Programme on Vaccination will probably be necessary if administration of second and third doses is to be ensured. Fortunately, a natural process of urbanisation is also having a beneficial effect on the black carrier rate in South Africa, as urban carrier rates tend to be much lower than those in rural area. Within the next 20 years, therefore, there should be a great reduction in the numbers of acute HBV infections and new carriers. However, it will take much longer before there is any substantial impact on the burden of the longterm sequelae of HBV infection--that is, cirrhosis and hepatocellular carcinoma.

Hepatitis B virus strains in Thailand: genomic variants in chronic carriers

Genetic heterogeneity of the hepatitis B virus (HBV) has been shown to influence the serological pattern and clinical picture in HBV infection. Thailand has a high transmission rate of HBV, but the molecular epidemiology of HBV strains circulating in this region was hitherto unknown. In this study, the HBV strains from 34 Thai HBsAg-positive patients were investigated. In a proportion of these samples, an antigenically important region of the S gene (n = 18), and the pre-S2 and precore genes (n = 15) were sequenced after PCR amplification. Four strains had in-frame deletions of an upstream region of the pre-S2 gene, with all deletions ending at the same nucleotide. In one of three anti-HBe positive strains without a translational stop at codon 28 of the precore gene, there was a one nucleotide insertion in the precore gene. This insertion would cause a frame shift and result in a nonsense protein being expressed, thus providing one explanation for the lack of HBeAg in this patient. Several rare or unique amino acid changes in the region between residues 120 and 161 of the S protein were found. Glycine 145 was changed to alanine in one strain, and this position showed an apparent mixture of glycine and arginine in another. In total, 10 strains displayed unexpected changes that were not related to the normal variability between subtypes or genetic subgroups. It is concluded that there is considerable heterogeneity in HBV strains in Thailand and that this could have clinical and epidemiological importance in a region with high HBV transmission rates.

Selection of a precore mutant after vertical transmission of different hepatitis B virus variants is correlated with fulminant hepatitis in infants

The incidence of perinatal transmission of hepatitis B virus (HBV) depends on the HBeAg/anti-HBe status of the mother. While children of HBeAg-positive mothers have a 90% probability of acquiring a chronic hepatitis B virus carrier state, babies of anti-HBe-positive mothers are more likely to develop fulminant hepatitis within the first 3 to 4 months of life. There is evidence that precore (pre-C) mutations of the HBV can be associated with fulminant hepatitis. The pre-C region was therefore examined in sera from nine infants with fulminant hepatitis after vertical transmission, one HBeAg-positive and seven anti-HBe-positive mothers by polymerase chain reaction (PCR) and direct sequence analysis. In five mother/infant pairs the virus populations were characterized in addition by analysing clones of the amplified products. All mothers were infected with two or four variants of HBV with mutations at different positions of the preC genome including position 1896, which results in a stop codon. While the precore stop codon was detected in a portion of the virus populations of the HBeAg-positive and of four anti-HBe-positive mothers the dominating viral strain was represented by the wild type virus in three. In contrast, the virus populations of all babies showed the 1896 precore variant as the prevalent virus strain during the phase of active disease. In the surviving baby only wild type sequences were detected after recovery. Subtype ayw was found in all mothers and infants and adw2 was present in three mothers and in the surviving child. The findings suggest that all mothers carried a wild type HBV population with a certain number of different HBV variants. After transmission of the mixed virus population a selection process was started in the baby. The association of subtype ayw with the precore mutations and with the fatal outcome of the hepatitis B might be the result of a directed selection of this variant with a particular advantage in the viral life cycle.

Analysis of hepatitis B virus precore variants in hepatitis B e antibody-positive patients treated with prednisone plus interferon

To assess the effects of prednisone and interferon on the distribution of hepatitis B virus (HBV) precore mutants, nine hepatitis B e antibody (HBeAb)-positive patients with HBV chronic infection were studied. Patients were treated with prednisone (30 mg day-1 for 4 weeks, followed by 20 mg day-1 for 2 weeks and by 10 mg day-1 for 1 week), followed by recombinant interferon-alpha (15 MU thrice per week) for 6 months, without a clearance period. The HBV precore region was amplified by polymerase chain reaction (PCR) and distribution of the precore mutants was determined by hybridization of PCR products. Moreover, the glucocorticoid-responsive element (GRE) was sequenced to determine whether changes in the sequence were produced at the end of prednisone treatment. During prednisone treatment, changes in alanine transaminase (ALT) were observed in only two patients, in who ALT decreased to nearly normal values. In three patients ALT normalized at the end of interferon treatment. At baseline, wild-type HBV alone was detected in one patient, while seven patients were infected by a mixture of wild-type and precore mutants, predominantly wild type. At the end of prednisone treatment, two patients were infected by only wild-type HBV. The proportion of precore mutants decreased in three cases, while no changes were observed in three. At the end of interferon treatment, the precore mutant proportion decreased in the three responders, while tending to increase or remain unchanged in the rest. No significant changes in GRE sequence were found as a result of prednisone treatment. Our results would appear to confirm the role of the immune system in the selection of precore mutants.

Hepatitis B virus precore/core variation and interferon therapy

Precore/core genes from hepatitis B e antigen (HBeAg)-positive and antibody to HBeAg (anti-HBe) positive individuals with active hepatitis have been analyzed to search for correlations with response to interferon before and after treatment. Pretreatment, no precore stop codon mutants were detected, even at the 3% level, in HBeAg-positive responders or nonresponders. In anti-HBe-positive patients, precore mutants did not influence response. No significant core amino acid variability was observed in HBeAg-positive patients, irrespective of interferon response. However, anti-HBe-positive cases had multiple core protein substitutions, mostly in B- ant T-helper cell epitopes, but responders had fewer (P = .02 for responders versus nonresponders and reactivators). None of four responders, three of seven reactivators, and three of three nonresponders had mutations within the major T-helper epitope from aa50 to aa69 (P = .03). Precore mutants appeared in eight of nine natural seroconverters compared with 3 of 10 interferon-induced anti-HBe seroconverters (P = .01). Those in whom precore wild-type remained after treatment often tested negative in the last available sample using polymerase chain reaction (PCR), whereas emergence of mutants led to ongoing viremia in all cases. In anti-HBe-positive cases, precore sequences remained stable during therapy, except for 2 cases in whom a precore mutant appeared accompanied by reactivation. In the core protein, anti-HBe-positive cases selected a mean of 3.5, 1.6, and 1.7 amino acid substitutions in responders, nonresponders, and reactivators respectively (P = NS). In conclusion, core but not precore sequence before therapy may predict response. Appearance of precore mutants during therapy usually predicts failure to clear virus but substitution in core does not influence outcome.

Clinical relevance of mutations in the precore genome of the hepatitis B virus

A stop codon in the precore genome of the hepatitis B virus (HBV) in anti-HBe positive HBV carriers may be associated with a more progressive form of HBV infection. Earlier studies, however, were mainly performed in patients from the Mediterranean area who had severe infection. The aim of this study was to evaluate the prevalence of precore mutants in an unselected population living in northern Europe. Twenty of 42 of these patients are infected predominantly with a virus strain, which has the typical stop codon in the precore genome, characterised by a mutation at base 83. In six patients there was an additional G to A mutation at base 86 of the precore genome. Statistical analysis showed no difference between the patients with or without a stop codon in the precore genome. When patients with a double mutation at base 83 and 86 of the precore genome were compared with the other anti-HBe positive HBV carriers, however, the corresponding clinical data were worse. Therefore we suggest, that it is not the stop codon in the precore gene itself, but the occurrence of a double mutation at bases 83 and 86, which is associated with a more severe course of disease in anti-HBe positive HBV carriers.

Hepatitis B virus precore mutants in HBeAg carriers with chronic hepatitis treated with interferon

Precore mutants of hepatitis B virus (HBV) were looked for in 18 hepatitis B e antigen (HBeAg) carriers who were treated with recombinant interferon-alpha (rIFN) and the results were compared with those obtained in 12 untreated carriers who underwent spontaneous HBeAb seroconversion. Molecular analysis of the HBV precore region was carried out by polymerase chain reaction (PCR) amplification and direct sequencing. Precore mutants with a stop codon at codon 28 were detectable at baseline in 19/30 carriers. However, wild-type strains predominated in the baseline sera of both treated (n = 16) and untreated (n = 10) patients. Sera from the remaining four patients contained predominantly or exclusively mutant virions. Following IFN treatment, there was a shift from the wild-type pattern to the mutant pattern in all patients, with the precore pattern prevailing in long-term responders (six out of nine) compared with the non-responders (none of nine). The wild-type pattern predominated among the non-responders (eight vs three), suggesting that the long-term response to IFN was associated with take-over of precore mutants. There were no relationships between any pretreatment precore molecular pattern and disease severity or outcome of treatment. Precore mutants also took over in 10 of the 12 untreated patients (83%), who underwent spontaneous HBeAb seroconversion. Thus, a shift from wild-type to precore mutant pattern occurs in most Italian patients undergoing IFN-induced or spontaneous HBeAb seroconversion.

Fulminant hepatitis caused by a hepatitis B virus core region variant strain

We studied the viral genome of a hepatitis B viral strain isolated from a patient with fulminant hepatitis. The patient was followed from prior to the rise in transaminases until she recovered. The precore and core regions of the viral strains were sequenced before and after the illness via the polymerase chain reaction and subcloning methods. Prior to her clinical illness, a strain with precore wild-type sequence and core mutations corresponding to amino acid residues 77 and 113 was noted in large quantities. With the onset of hepatitis, this core variant completely disappeared. Very low titers of precore and core wild or partial core deletion strains remained 1 month later. The core variants described may have contributed to the severe host immune reaction, fulminant hepatitis and immune-mediated viral clearance. Such variants appeared to have been eliminated, and wild and core-deleted virus that lacked the peculiar mutations remained.

Genetic heterogeneity in the precore region of hepatitis B virus in hepatitis B e antigen-negative chronic hepatitis B patients: spontaneous seroconversion and interferon-induced seroconversion

To elucidate the relationship between the clinical severity of chronic liver disease and the precore mutations in hepatitis B e antigen (HBeAg)-negative hepatitis B virus (HBV) carriers, mutations were investigated in the precore region of HBV DNA in 20 chronic hepatitis B patients who seroconverted either spontaneously or after the administration of alpha-interferon (IFN), and 5 asymptomatic carriers. The precore mutation with a stop codon at nucleotide 1896 was found in all patients, irrespective of the histology and in all asymptomatic carriers. The second mutation at nucleotide 1899 was found in 40% of cases studied but always followed by the first mutation at nucleotide 1896. The mixed viral infection of precore mutant and wild-type HBV virus was found in 40% of seroconverted cases after IFN treatment and in sera of HBV carriers obtained within a year after the spontaneous seroconversion. These data suggest that the precore mutants prevail over wild-type HBV in all HBeAg-negative HBV carriers within several years after the seroconversion, but their prevalence could not confine the clinical severity of chronic liver disease.

Precore and X region mutants in hepatitis B virus infections among renal dialysis patients

Hepatitis B virus (HBV) variants containing mutations within the X and the precore regions of the viral genome were demonstrated by polymerase chain reaction (PCR) amplification and DNA sequencing in renal dialysis patients with different serological patterns of HBV infection. Among carriers, X region deletion mutants predominated in patients who lost hepatitis B e antigen (HBeAg), or developed anti-HBe, but not in persistently HBeAg-positive patients. The precore region remained wild type in all carriers whether or not they seroconverted from HBeAg to anti-HBe. The frequency of precore and X region mutants was greatest among non-carrier patients with viral antibodies as the only indication of infection and among patients with non-A, non-B hepatitis (NANBH), suggesting an inverse relationship between the presence of wild type HBV markers and the presence of HBV mutants. Furthermore, the detection of one but not the other mutation in many serum samples suggests that these mutations are independently selected for during infection. Finally, the absence of HBV DNA in 21 'uninfected' dialysis patients with normal transaminases and no viral serology, suggests that replication of these mutants is associated with hepatitis. These results have important implications for HBV screening and treatment, as well as for the pathogenesis of chronic infection.

Nucleotide sequence analysis of precore and proximal core regions in patients with chronic hepatitis B treated with interferon

The aim of the study was to estimate the prevalence of HBeAg defective mutants among patients with chronic hepatitis B (CHB) in the United States and to study the effect of interferon-alpha (IFN-alpha) on determining the occurrence of mutations in the HBV precore and proximal core regions. Twenty CHB patients who were treated with IFN-alpha were studied. Initially, all were HBV DNA positive by dot-blot hybridization; 17/20 were HBeAg positive, and 3/20 were anti-HBe positive. The precore (87 nt) and proximal core (81 nt) regions were sequenced after PCR amplification by the dideoxy chain termination method. In pretreatment sera, 15/20 patients harbored wild-type HBV only, while in 5/20 at least one nucleotide substitution was found. Mutations that prevent HBeAg synthesis were found in three patients, all of whom had G-to-A substitution at nt 1896 and two of them were anti-HBe positive. Follow-up sera were available in 18 patients. With respect to pretreatment specimen, 15/18 patients had no changes in the sequenced regions after therapy. Sequence changes were observed in the remaining three patients: In one an HBeAg defective strain was replaced by a wild-type strain; in the second a wild-type strain was replaced by an HBeAg defective strain; and in the third two mutations changing the deduced amino acid sequence of the core protein developed in the wild-type strain. In conclusion, most of our patients (85%) were initially infected by HBV strains having no mutations that prevented HBeAg synthesis. IFN-alpha therapy infrequently resulted in the appearance of mutations in the precore and proximal core regions.

Selective transmission of variant genomes from mother to infant in neonatal fulminant hepatitis B

Hepatitis B virus (HBV) nucleotide sequences isolated from mother/child pairs were analyzed in three cases of neonatal fulminant hepatitis B (FHB). Heterogeneous HBV sequences consistent with both adw2 and ayw subtype were found in all three mothers. In one case, in which the child survived, both subtypes were transmitted. By contrast, only the ayw subtype was present in the two other children with a fatal course of FHB. In one fatal case, studied in greater detail, multiple HBV variants (viral quasi-species) were identified in both mother and child. A direct sequence comparison showed that only a subfraction of the virus pool from the mother was transmitted and that multiple new mutations emerged in the child. These data suggest that a minor HBV subpopulation from the mother may prevail as the dominant species in the child and that neonatal FHB is associated with the selection of mutant strains.

Different prevalence of precore mutants in five members of a hepatitis-B-virus-infected family: evidence for a precore variant type in an asymptomatic anti-HBs patient

Chronic active hepatitis B (CAH-B), anti-HBe (+) has been associated with a hepatitis B virus variant carrying a stop codon at the distal pre-C region that prevents HBeAg synthesis. We analyzed the HBV DNA pre-C region in five members of a Turkish family. The mother presented an anti-HBe (+) CAH-B and the four children different hepatitis B virus serological and clinical profiles. The pre-C region was analyzed by cloning after DNA amplification in sera and peripheral blood mononuclear cells. A method for rapid screening of a large number of cloned polymerase chain reaction products was developed for the presence of the most frequent pre-C mutations (G to A substitution at nucleotide position 1896 and 1899). At least 60 independent clones were tested for each patient by selective oligonucleotide hybridization using non-mutated (M0), one (M1) and two (M2) point-mutated probes. Results were confirmed by sequencing. The mutation 1896 was present in 91% of DNA clones from the mother. The same mutation was also found in 85% of the clones in the youngest child (D), but in less than 10% of the clones from children A and C. Only the pre-C wild-type strain was observed in child B. X gene deletions (3 to 20 nt) were also present in some clones from the mother and children A, B and C. No significant difference between serum and peripheral blood mononuclear cells concerning the viral population was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatitis may precede the occurrence of precore region mutation in hepatitis B virus genome during infection in young carriers

To understand when the mutation with a stop codon of precore region in hepatitis B virus genome occurs, the prevalence of the mutation of viral DNA clones propagated from sera of school-age carriers was investigated with respect to hepatitis B e antigen (HBeAg)/anti-HBe and sequential changes of mutants along HBeAg seroconversion were analyzed. Of 32 carriers aged 8-18 years, 14 HBeAg(+) patients had 2.2% mutant clones, whereas 8 patients with low titer anti-HBe had a higher rate of 18.1% (P < 0.01) and the highest rate of 61.3% was found in 10 patients with high anti-HBe titer (P < 0.001). By contrast, the amount of viral DNA decreased significantly in patients with anti-HBe. Sequential analysis in six cases revealed three types of seroconversion with time difference of the emergence and increase of mutant clones. It is concluded that mutation occurs at a relatively young age and increases along time and/or HBeAg seroconversion. Hepatitis might precede or accelerate the emergence and increase of mutant population which might be predictive of sustained resolution of the disease.

Precore region mutation in hepatitis B virus genome in early stage of infection: a study in hepatitis B e antigen-positive young carriers

To determine when the precore mutation at the 83rd nucleotide occurs, leading to the formation of a stop codon in the hepatitis B virus genome in carriers, which would indicate the presence of antibody to hepatitis B e antigen (anti-HBe), we investigated this mutation by direct sequencing and subcloning in 22 young hepatitis B antigen (HBeAg) (+) carriers. These subjects were 7-17 years old and were found during a survey for hepatitis B surface antigen (HBsAg) in three elementary schools, a junior high, and a senior high school. None of these carriers had clinical manifestations, although one-third of them had elevated serum alanine aminotransferase levels. All were HBeAg-positive by radioimmunoassay (RIA), and 6 of them had preserved titers of anti-HBe at the same time. Precore mutations were found in 4 subjects (18.2%), with predominance of the wild type. Although 3 of these 4 had preserved titers of HBeAb, the other had no HBeAb titers. In an other 3 subjects with preserved titers of HBeAb, the precore mutation was not detected, even after the subcloning of viral DNA. The remaining 15 subjects with HBeAg showed no precore mutation. Subjects with ALT levels exceeding 100 IU/l were all HBeAg-positive without the mutation. It was clear that the precore mutation itself occurred in the subjects at an early age during the course of infection. However, the chronological relationship between the emergence of the precore mutation and the onset of hepatitis requires further study.

Mutations in the pre-core region of hepatitis B virus serve to enhance the stability of the secondary structure of the pre-genome encapsidation signal

We conducted a large-scale survey to determine the frequency and clinical significance of mutations in the pre-core region of hepatitis B virus (HBV). Sera from 263 patients with chronic HBV infection were analyzed by direct sequencing of PCR-amplified HBV DNA. Four major missense/nonsense mutations (M) were found: (M1) C-->T at nucleotide position 1856, Pro-->Ser at codon 15; (M2) G-->A at position 1896, Trp-->stop at codon 28; (M3) G-->A at position 1898, Gly-->Ser at codon 29; and (M4) G-->A at position 1899, Gly-->Asp at codon 29. The commonest conserved mutation was M0: T-->C at position 1858, Pro-->Pro at codon 15. We found that M1 and M2 were mutually exclusive, M3 was only found in association with M1, and M4 was predominantly found in association with M2. All patients with M1 but none of those with M2 had M0. The invariable coexistence of certain mutations in codon 15 and codons 28 and 29 and the mutual exclusion of other mutations in these two noncontiguous regions is related to the stem-loop structure of the pre-genome encapsidation sequence located in the precore/core region. M2 and M4 enhance the stability of the stem by providing two additional paired sites. M1 destroys an existing base pair. However, M1 only occurred in the presence of M0, which provides an extra paired site, and 50% of patients with M1 had M3, a compensatory mutation that restores base pairing at this site. Our data support the proposed secondary structure of the pre-genome encapsidation sequence. The primary function of the mutations in the pre-core region is to enhance stability of this secondary structure to ensure perpetuation of viral replication.

Hepatitis B virus precore mutation and fulminant hepatitis in the United States. A polymerase chain reaction-based assay for the detection of specific mutation

Hepatitis B virus (HBV) variants with precore mutation(s) resulting in the absence of HBeAg production have been associated with the occurrence of fulminant hepatitis in Japan, Israel, and southern Europe, where the prevalence of this HBV strain appears common. In areas such as United States, where HBV infection is not endemic, the role of this mutant virus in fulminant hepatitis is unknown. We developed an amplification refractory mutation detection system to detect specifically the presence of the G to A mutation at nucleotide position 1898, which is the most frequently observed mutation resulting in a precore stop codon. In addition, this method provided a quantitative measurement of the relative ratio of one strain to the other. Using this system, we tested HBV strains for the presence of the stop codon mutation in sera from 40 cases of fulminant hepatitis B occurring in the United States. Serum HBV DNAs from 28 patients were analyzed successfully. A mixture of wild-type and mutant strains in various ratios were observed in 15 patients, wild type exclusively in 11, and mutant exclusively in 2. Four of these patients had undergone liver transplantation for HBV-associated cirrhosis and developed fulminant HBV-associated hepatitis after transplantation. Pre- and posttransplant serum samples from one patient were analyzed: a mixture of wild-type and mutant HBV strains was detected in both samples. Our study demonstrated that both wild-type and mutant HBV strains are associated with fulminant hepatitis, and that in some patients in the United States, factors other than precore mutations contribute to the development of fulminant hepatitis.

Problem hepatitis viruses: the mutants

Genetic variations in the known human hepatitis viruses are probably the result (a) of high viral replication rates and poor or absent proofreading ability intrinsic to RNA viruses (HAV, HCV, HDV, HEV) and (b) to a DNA virus (HBV) that uses a reverse-transcription mechanism for genomic replication. Nucleotide substitutions, deletions, duplications, insertions, and rearrangements resulting in amino acid changes may have no consequences, may impair replication, change host susceptibility, or may lead to escape from immune attack. Genetic diversity has been identified in each of the known hepatitis viruses. The importance of mutant viruses in pathogenicity, immunity, natural history, clinical outcomes, vaccine production, and responsiveness to treatment has emerged as an area for intensive study.

Hepatitis B virus genotype A rarely circulates as an HBe-minus mutant: possible contribution of a single nucleotide in the precore region

The emergence of HBe-minus hepatitis B virus (HBV) mutants, usually through a UAG nonsense mutation at codon 28 of the precore region, helps the virus to survive the anti-HBe immune response of the host. Host and viral factors that predispose to the emergence of such mutants are not well characterized. The fact that the precore region forms a hairpin structure essential for the packaging of viral pregenomic RNA may explain the extremely high prevalence of the UAG mutation at codon 28. It converts a wobble U-G pair in the packaging signal between nucleotide 3 of codon 15 (CCU) and nucleotide 2 of codon 28 (UGG) into a U-A pair. Since genotype A of HBV has a CCC sequence at codon 15, the UAG mutation would, instead, disrupt a C-G pair present in the wild-type virus. This alteration was shown by transfection experiments to greatly compromise the packaging of pregenomic RNA. The implication of this finding was elucidated by molecular epidemiological studies. Genotype A was found to be the most prevalent genotype in the wild-type virus populations in France but was found in only 1 of the 46 isolates of HBe-minus mutants found there. These mutants were contributed chiefly by genotype D, the second most prevalent genotype in France, which is characterized by a CCU sequence at codon 15. The role of the single nucleotide at codon 15 was confirmed by the finding of the single genotype A isolate in which both wild-type and mutant viruses were present. Interestingly, nearly all of the mutants had a codon 15 sequence of CCU instead of the CCC present in the wild-type viruses. Our results suggest that genotype A of HBV rarely circulates as HBe-minus mutants, probably because of a requirement for a simultaneous sequence change at codon 15. These data, together with the virtual absence of genotype A in the Chinese samples examined, may provide some insights into the uneven prevalence of HBe-minus mutants in the world.