Prevalence of precore-defective mutant of hepatitis B virus in HBV carriers

Tracking the naturally occurring mutations across the full-length genome of hepatitis B virus of genotype D in different phases of chronic e-antigen-negative infection

Hepatitis B e-antigen (HBeAg)-negative chronic HBV infection is highly prevalent in several parts of the world, including India, with the clinical spectrum ranging from inactive carrier (IC) state to chronic 'e-negative' hepatitis B (CHB) and culminating in advanced liver disease such as cirrhosis (LC). The present study has for the first time investigated the natural diversity of HBV belonging to genotype D in treatment-naïve Indian patients representing the above phases of HBeAg-negative infection to identify candidate mutations associated with each disease state. Studies of full-length HBV/D sequences revealed that the progressive accumulation and persistence of mutations in basal core promoter, negative regulatory element, Pre-core region, the B- and T-cell epitopes of X protein as well as deletions in the PreS region contribute significantly to disease progression from IC through CHB to LC. In addition, the development of CHB was associated with a significant increase in viral variants characterized by mutations in enhancer II, preS1 promoter, T-cell epitope of core and B-cell epitope region of PreS1. While few of the mutations were previously reported in the context of HBV genotypes B and C, others had not been documented before. Our results thus highlight a distinct pattern of mutation in HBV/D that may help in predicting clinical outcomes of HBeAg-negative infection and have implications for better clinical management of the patients.

T cell responses and viral variability in blood donation candidates with occult hepatitis B infection

BACKGROUND & AIMS

Occult HBV infection (OBI) is defined by the presence of HBV DNA in the liver and/or serum and negative HBsAg testing. Since the implementation of highly sensitive HBV DNA screening, OBI is also detected in healthy blood donors. The aims of this study were to investigate HBV-specific immune responses and genetic variability in donors with OBI, established by HBV DNA in serum.

METHODS

HBV-specific T-cell responses to HBV antigens were tested in 34 OBI donors by IFN-γ ELISpot, cytometric bead array, and intracellular cytokine staining. As comparison populations, 36 inactive HBV carriers, 22 donors with spontaneously resolved HBV infection, 24 vaccinated donors, and 25 seronegative donors were also included. Surface, pre-S, and pre-c/core genes from 44 genotype D isolates (24 OBI and 20 HBsAg-positive) were sequenced.

RESULTS

The immune response of OBI donors to the 3 HBV antigens was 29-41%, similar to the response in subjects with resolved HBV infection and higher than that in HBsAg-positive subjects. On sequence analysis, OBI donors presented a higher HBsAg mutation rate than HBsAg-positive subjects. Mutations were clustered in the major hydrophilic region of HBsAg, and no stop codons or relevant mutations that could affect antigen formation or detection were observed.

CONCLUSIONS

Our results suggest that immune response can suppress viral replication to low levels and HBsAg expression to undetectable levels in OBI blood donors. Relevant mutations were not found in the genomic HBsAg coding region. Hence, the fact that HBsAg was not detected in OBI is likely due to low HBsAg production, rather than to a failure of laboratory reagents.

Molecular methods in the diagnosis and management of chronic hepatitis B

Chronic hepatitis B (CHB) infection remains a major global problem but the recent advances in molecular methods have revolutionized the diagnosis and management of CHB. Hepatitis B virus (HBV) DNA quantitation is the most useful molecular marker for the diagnosis and management of CHB. There is increasing evidence that the clinical outcome and efficacy of antiviral therapy for CHB could vary with the infecting HBV genotype, core promoter and precore mutations. Early identification of drug resistance is imperative in the management of CHB. The molecular methods for HBV DNA quantitation, HBV genotyping, the identification of mutants, genotypic and phenotypic methods for monitoring drug resistance and their utility and limitations for use in the diagnosis and monitoring of CHB are discussed in this article.

Clinical significance of genotypes and precore/basal core promoter mutations in HBV related chronic liver disease patients in North India

PURPOSE

Data on genotypes, basal core promoter (BCP) and precore mutants of hepatitis B virus and their association with different HBV related liver disease have been studied inadequately and are controversial. Thus, the aim of this study was to determine the incidence of BCP and precore HBV mutants and their relationship with HBV genotype and different stages of HBV related liver disease in North Indian patients.

METHODS

A total 273 patients with different stages of HBV related liver diseases were enrolled. Nested polymerase chain reaction (PCR) was used to amplify the BCP/PC regions. RFLP and direct sequencing were performed to validate the mutations identified in these regions. HBV genotyping was accomplished by multiplex PCR.

RESULTS

Genotype D was the predominant genotype found in each of the various HBV related liver diseases. The BCP mutation was found significantly more often in inactive carriers and compensated cirrhosis as compared to the other groups. The BCP mutation was present in 29.1% of patients with genotype D versus 17.1% with genotype A (P = 0.001). The precore mutation was also more frequently observed with genotype D compared with genotype A (36.9 vs. 4.8%, P = 0.0007).

CONCLUSION

Genotype D is predominant in North Indian patients. The BCP and precore mutations occur in one-third of HBV positive patients in association with the genotype D. We did not find any correlation with severity of liver disease with genotypes and mutations.

Analysis of the entire nucleotide sequence of hepatitis B causing consecutive cases of fatal fulminant hepatitis in Miyagi Prefecture Japan

We encountered five consecutive patients with fulminant hepatitis induced by acute hepatitis B virus (HBV) infection in 2000--2001 in Japan. They had not had previous contact each other, and were referred to us from different hospitals. Although a 69-year-old woman could be rescued by intensive internal treatment, the four patients died. We analyzed the partial (nt 278-646) and entire nucleotide sequences of the HBV obtained from them, and their divergences were 0-0.3% and 0-0.2%, respectively. The results suggested that they had been infected with the same HBV isolates. The isolates belonged to genotype B and subgenotype B2 on the phylogenetic tree analysis (AB302942-AB302946). As for the nucleotides sequences of them, previously reported mutations of G1896A, A1762T, and G1764A were present. Amino acid analysis revealed that previously reported Ile97Leu and Pro130Non-Pro in the core region and Trp28Stop in the precore region were present. As for the entire nucleotide sequences among B2, AB302942 showed low divergences with AF121245 and AB073834 (1.7%), and X97850 from patients with fulminant hepatitis (3.2%). We compared the two consensus nucleotides derived from AB302942 and X97850 (fulminant hepatitis) versus AY121245 and AB073834 (non-fulminant hepatitis), which revealed a difference in nt 1,504 located in the P and X region. Nucleotide 1,504 was C for isolates from fulminant hepatitis and G for non-fulminant hepatitis, and it was recognized among most of the isolates belonging to B2 registered on GenBank. Further studies could disclose the mechanism of severe inflammation of liver that finally leads to fulminant hepatitis.

Analysis of the entire nucleotide sequence of hepatitis B virus genotype B in the Philippines reveals a new subgenotype of genotype B

The entire nucleotide sequences were determined for hepatitis B virus (HBV) genotype B (HBV/B) genomes extracted from five patients in the Philippines and designated GenBank AB219426, AB219427, AB219428, AB219429 and AB219430. The serotype of the first four isolates was ayw and that of GenBank AB219430 was adw. Divergences of entire sequences were 1.0-2.0 % between the first four isolates and 3.8-4.2 % between these four and GenBank AB219430. Phylogenetic-tree analysis revealed that, worldwide, HBV/B comprises five subgenotypes: B1, B2, B3, B4 and the new Philippines group, designated B5. Divergences of the entire genome sequences between four isolates in subgenotype B5 and isolates from other countries (subgenotypes) were 4.4-4.8 % with Vietnam (B4), 2.9-3.5 % with Indonesia (B3), 4.7-5.1 % with China (B2) and 5.4-6.0 % with Japan (B1). Similarly, GenBank AB219430 showed the lowest divergences: 3.4 % with the isolate from Indonesia (B3), 5.0 % with Vietnam (B4), 5.4 % with China (B2) and 6.1 % with Japan (B1). This is the first report of entire nucleotide sequences of HBV/B from the Philippines and the results show that these sequences belong to a new subgenotype, B5. The present study identified that HBV/B isolates throughout the world are divided genetically into five subgenotypes, the relationships between geographical distances and the genetic distances of HBV/B being well-correlated.

Alternative peptide-fusion proteins generated by out-of-frame mutations, just upstream ORFs or elongations in mutants of human hepatitis B viruses

By various means including out-of-frame mutations, just upstream ORFs and elongations, additional peptide fusions could be generated by mutants of Human Hepatitis B Virus (HBV). Numerous frameshift mutations inducing long alternative open reading frames have been evidenced in all HBV genes. Interestingly, these mutants are frequently detected in severe liver diseases, but seldom in asymptomatic carriers. The high level of conservation of some of these sequences in spite of the fact that they could be generated by different types of mutations, as their presence in mutants found on various continents, suggest that these mutations could play a role. These mutants could combine two advantages, that related to the loss of a part of a wild-type protein and that related to the putative advantage conferred by the additional sequences. In addition, in numerous Asian genomes (more than 300 to date) pre-X or pre-pre-S regions were found just upstream to, respectively, the X and the pre-S1 genes. These two regions are translated with their respective genes in frame and recent studies have evidenced the transactivating role of the corresponding proteins. With some exceptions, these regions are genotype- and serotype-specific (C/adr). In addition, these mutants have been found principally in patients with severe hepatitis diseases, for example, hepatocarcinoma in more than one third of the cases. As additional sequences generated by HBV variants may be relevant for viral life cycle, persistence and pathogenesis, further investigations are necessary to give a clearer picture of the subject.

The precore mutation is associated with severity of liver damage in Brazilian patients with chronic hepatitis B

BACKGROUND

The clinical relevance of the G1896A precore mutation in chronic hepatitis B is still poorly understood.

OBJECTIVES

To assess the frequency of G1896A precore mutation in Brazilian patients with chronic hepatitis B, as well as its relation to the viral genotype, serum HBV-DNA levels and liver damage.

STUDY DESIGN

Fifty chronic hepatitis B patients (29 HBeAg-negative and 21 HBeAg-positive) were studied. HBV-DNA was quantified by the Amplicor HBV Monitor test and precore region and S gene were amplified and submitted to automatic sequencing. The histological activity index (HAI), degrees of hepatic fibrosis and distribution of core antigen (HBcAg) in hepatocytes were determined.

RESULTS

Precore mutation occurred in 1/21 (4.8%) HBeAg-positive patients and in 17/29 (58.6%) HBeAg-negative (p < 0.0001). Genotype D was identified in 56.5%, genotype A in 41.3%, and genotype F in 2.2%. The frequency of genotypes D and A, as well as serum levels of ALT and HBV-DNA were similar in patients infected with wild type and with precore mutant. Patients infected with precore mutant presented a higher frequency of moderate/severe HAI (p: 0.03) and moderate/severe fibrosis and cirrhosis (p: 0.03) than those infected with wild type. There was no association between G1896A mutation and cytoplasmic expression of HBcAg.

CONCLUSIONS

Precore mutation was frequent among Brazilian subjects with chronic hepatitis B and its presence was associated with greater severity of liver disease.

High frequency of the 1896 precore mutation in patients and blood donors with hepatitis B virus infection from the Indian subcontinent

AIM

Hepatitis B virus (HBV) e antigen (HBeAg)-negative variants are reported to harbor 1896 precore mutants, and predict a worse clinical outcome. The aim of this study was to estimate the incidence of a precore mutation (1896) in both patients with chronic hepatitis B (CH-B) infection and blood donors in a tertiary care hospital in south India.

METHODS

One hundred and twenty-two consecutive HBV DNA-positive CH-B patients (group I) and 102 HBsAg-positive 'healthy' blood donors (group II) were recruited. Samples found to be positive for HBV DNA were further studied. A nested PCR was used for the detection of HBV DNA. The 1896 precore mutation was detected using PCR-restriction fragment length polymorphism (RFLP). Nucleotide sequencing was performed on representative samples to confirm PCR-RFLP findings. The study population was stratified comprising: group IA: 17 HBeAg-positive CH-B patients; group IB: 105 HBeAg-negative CH-B patients; group IIA: 12 HBeAg-positive blood donors; and group IIB: 55 HBeAg-negative blood donors.

RESULTS

There was no significant difference in the HBeAg-positive status between groups I and II. Significantly higher levels of alanine transaminase (ALT) were seen in groups IA and IB than in groups IIA and IIB, respectively (p = 0.033; p = 0.004). A significantly higher proportion of CH-B patients (32.7%) were positive for anti-HBc IgM compared with the blood donor groups (10.4%; p = 0.0006). Among the HBeAg-negative subjects, 69% of the CH-B patients and 65% of the blood donors showed evidence of 1896 precore mutant. This infection included the 1896 mutant exclusively or mixed infection involving the 1896 mutant and 1896 wild-type.

DISCUSSION

The absence of detectable HBeAg in most of the viremic blood donors and patients emphasizes the need for HBV DNA testing irrespective of HBeAg status. Mixed infection was detected in a higher proportion (42.6%) of CH-B patients than in blood donors (26.8%; p = 0.031). Among those with mixed infection, a significant proportion (44.2%) of CH-B patients, had ALT levels greater than the upper limit of normal (ULN), as compared with the blood donor groups (16.6%; p = 0.036).

CONCLUSIONS

The majority of CH-B patients and blood donors were negative for HBeAg despite their positive HIV DNA status. About two-thirds of the HBsAg-positive blood donors were viremic. Mixed infection was detected more frequently in CH-B patients and appears to be associated with more pronounced liver damage, as indicated by increased ALT levels.

Uncommon mutation pattern of a hepatitis B virus isolate from genotype F infecting a patient with AIDS

OBJECTIVE

To study the genomic variations of a hepatitis B virus (HBV) isolate in a patient coinfected with human immunodeficiency virus type 1 (HIV-1) who developed severe hepatitis and died of AIDS.

METHODS

Two blood samples were collected, the first one during the asymptomatic phase of HIV-1 infection, and the other, 3 years later, few months before the death of the patient. Both samples were HBsAg and anti-HBe positive. Pre-S/S and precore-core genome regions were PCR amplified and analyzed.

RESULTS

The HBV isolate belonged to genotype F, cluster IV. A number of unique amino acid substitutions were found in the surface antigen gene and the overlapping polymerase coding region of HBV genomes derived from both samples. However, these substitutions reflected natural variations rather than mutations of clinical significance. The precore stop codon mutation A(1896) was present in both genomes. Furthermore, the HBV genome derived from the second, but not first sample, showed two out-of-frame core interval deletions, one and 103 nucleotides in length, respectively.

CONCLUSIONS

This is the first report of an HBV isolate from genotype F with core internal deletions. Our results suggest an association between specific core mutations and the severe hepatitis developed by the patient.

Prevalência de genótipos e de mutantes pré-core A-1896 do vírus da hepatite B e suas implicações na hepatite crônica, em uma população da Amazônia oriental

A infecção pelo virus da hepatite B apresenta amplo espectro de manifestações clínicas. Objetivando conhecer os genótipos do HBV mais prevalentes e determinar a ocorrência da mutação pré-core A-1896, em uma população da Amazônia oriental, correlacionando com o diagnóstico clínico, foram selecionados 51 pacientes portadores crônicos de HBsAg e HBV-DNA positivos e divididos em três grupos: grupo A (n=14, pacientes assintomáticos); grupo B (n=20, sintomáticos HBeAg positivos) e grupo C (n=17, sintomáticos HBeAg negativos), sendo usado o sequenciador automático ABI modelo 377 para identificação de genótipos e mutantes pré-core. Os resultados evidenciaram o genótipo A como o mais prevalente, 81,8%, 89,5% e 93,7%, nos grupos A, B e C, respectivamente. A mutação pré-core A-1896 foi encontrada em 11,5% (3/26), sendo todos assintomáticos. Concluiu-se que na população estudada o genótipo A foi o mais prevalente e houve baixa ocorrência do mutante pré-core A-1896, ambos não se constituindo fatores agravantes da doença hepática.

Hepatitis B virus: prevalence of precore/core promoter mutants in different clinical categories of Indian patients

To determine the association of precore (Pre-C)/basal core promoter (BCP) mutants with clinical outcome of hepatitis B in Western India, 192 hepatitis B virus (HBV) infected individuals were investigated. HBV-DNA PCR positivity among asymptomatic hepatitis B surface antigen (HBsAg) positive carriers (61/100) was lower (P < 0.0001) than chronic hepatitis B (CHB), acute (P = 0.0001), and fulminant hepatitis B patients (P = 0.047). Pre-C status was based on restriction fragment length polymorphism (RFLP, n = 153) and sequencing (n = 118). Prevalence of Pre-C mutants was higher among carriers (23/61) than CHB (10/62, P = 0.0071) or acute (3/22; P = 0.037) patients. Children from carrier and CHB categories showed significantly higher circulation of Pre-C-wild than mutant HBV. Clinical manifestations were independent of BCP mutations (1762/64-T/A). Hepatitis B e antigen (HBeAg) negative CHB patients [62.5% (15/24)] were circulating wild HBV. Higher HBV-DNA levels were associated with chronic hepatitis and HBeAg positivity, whilst Pre-C mutant positives had lower levels. BCP mutations did not affect HBV-DNA levels. Multivariate regression analysis identified HBeAg (OR = 4.3) and Pre-C mutants (OR = 3.1) to be associated with chronic hepatitis and carriers respectively. In a separate sub-set analysis (n = 59), HBV-DNA level was identified as the only variable. In conclusion, chronic or fulminant hepatitis B was not associated with Pre-C or BCP mutants and switching over to Pre-C mutant was beneficial for the infected individual in maintaining disease free status for extended periods.

World-wide epidemiology of HBeAg-negative chronic hepatitis B and associated precore and core promoter variants

Hepatitis B is a serious disease that is endemic in many parts of the world. A significant proportion of patients with chronic hepatitis B (CHB) are infected with a variant form of the hepatitis B virus (HBV) which decreases or abolishes the production of hepatitis B e-antigen (HBeAg). The purpose of this literature review is to describe the epidemiology of HBeAg-negative CHB (e-CHB) worldwide. A literature search was conducted to identify studies pertaining to e-CHB and underlying variants (precore and core promoter). Fifty studies were included in our analysis. The median prevalence of e-CHB among patients with chronic HBV infection was 33% in the Mediterranean, 15% in Asia Pacific, and 14% in the USA and Northern Europe. The pre core stop codon variant was detected in a median of 60% (range 0-100%) of HBeAg-negative patients overall, 92% in the Mediterranean, 50% in Asia Pacific and 24% in the USA and Northern Europe. There were very few data on the prevalence of core promoter variants outside Asia where the median prevalence among HBeAg-negative patients was 77%. This literature review revealed that e-CHB is more common than previously suspected and that it is present worldwide with marked variations in the prevalence of associated HBV variants across different geographical regions. Additional research using population based samples of adequate size based on a consensus definition of e-CHB and using standardized HBV DNA assays is needed to better estimate the true prevalence of e-CHB and its associated HBV variants.

Molecular, immunological and clinical properties of mutated hepatitis B viruses

Hepatitis B virus (HBV) is at the origin of severe liver diseases like chronic active hepatitis, liver cirrhosis and hepatocellular carcinoma. There are some groups of patients with high risk of generation of HBV mutants: infected infants, immunosuppressed individuals (including hemodialysis patients), patients treated with interferon and lamivudine for chronic HBV infection. These groups are the target for molecular investigations reviewed in this paper. The emergence of lamivudine- or other antiviral-resistant variants, rises concern regarding long term use of these drugs. Infection or immunization with one HBV subtype confers immunity to all subtypes. However, reinfection or reactivation of latent HBV infection with HBV mutants have been reported in patients undergoing transplant and those infected with HIV. Mutations of the viral genome which are not replicative incompetent can be selected in further course of infection or under prolonged antiviral treatment and might maintain the liver disease. Four open reading frames (ORF) which are called S-gene, C-gene, X-gene and P-gene were identified within the HBV genome. Mutations may affect each of the ORFs. Mutated S-genes were described to be responsible for HBV-infections in successfully vaccinated persons, mutated C-genes were found to provoke severe chronic liver diseases, mutated X-genes could cause serious medical problems in blood donors by escaping the conventional test systems and mutated P-genes were considered to be the reason for chemotherapeutic drug resistance. This paper reviews molecular, immunological and clinical aspects of the HBV mutants.

Epidemiology of precore mutants of hepatitis B in the United Kingdom

A point mutation assay was used to study the codon 28 and codon 1 precore mutant status of 310 chronic hepatitis B carriers (82 HBeAg positive and 228 HBeAg negative). Fourteen of 228 (6%) of HBeAg negative carriers had high levels of serum HBV DNA. Nine of these were explained by precore variants, three by core promoter variants, and two were not explained by recognised precore changes. Nested PCR detected serum HBV DNA in 36% (82/228) of HBeAg negative carriers and 63% (52/82) of these had precore variants. Four of 82 (4%) of the HBeAg positive carriers had precore variants, all as mixed mutant/wild type populations and evidence indicated that these carriers were seroconverting. Overall 23% (52/228) of HBeAg negative carriers had both serum HBV DNA and codon 1 or 28 precore mutations. A sexual transmission event from an HBeAg negative carrier with a relatively low serum HBV DNA level (10(4)-10(6) genome copies/ml) and only core promoter mutations was observed. Despite high rates of variant carriage in the antenatal sub-group perinatal transmission was not observed. The results of direct sequencing on 45 carriers validated the point mutation assay and also showed that codon 28 mutations were only seen in carriers with the genotype CCT at codon 15. For the Caucasian population a higher prevalence of codon 28 mutations (13/25 or 52%) than expected was seen. Liver biopsy data indicated that there was no link between the presence or absence of precore mutants and the severity of liver disease.

Risk and management of blood-borne infections in health care workers

Exposure to blood-borne pathogens poses a serious risk to health care workers (HCWs). We review the risk and management of human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) infections in HCWs and also discuss current methods for preventing exposures and recommendations for postexposure prophylaxis. In the health care setting, blood-borne pathogen transmission occurs predominantly by percutaneous or mucosal exposure of workers to the blood or body fluids of infected patients. Prospective studies of HCWs have estimated that the average risk for HIV transmission after a percutaneous exposure is approximately 0.3%, the risk of HBV transmission is 6 to 30%, and the risk of HCV transmission is approximately 1.8%. To minimize the risk of blood-borne pathogen transmission from HCWs to patients, all HCWs should adhere to standard precautions, including the appropriate use of hand washing, protective barriers, and care in the use and disposal of needles and other sharp instruments. Employers should have in place a system that includes written protocols for prompt reporting, evaluation, counseling, treatment, and follow-up of occupational exposures that may place a worker at risk of blood-borne pathogen infection. A sustained commitment to the occupational health of all HCWs will ensure maximum protection for HCWs and patients and the availability of optimal medical care for all who need it.

Risk and management of blood-borne infections in health care workers

Exposure to blood-borne pathogens poses a serious risk to health care workers (HCWs). We review the risk and management of human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV) infections in HCWs and also discuss current methods for preventing exposures and recommendations for postexposure prophylaxis. In the health care setting, blood-borne pathogen transmission occurs predominantly by percutaneous or mucosal exposure of workers to the blood or body fluids of infected patients. Prospective studies of HCWs have estimated that the average risk for HIV transmission after a percutaneous exposure is approximately 0.3%, the risk of HBV transmission is 6 to 30%, and the risk of HCV transmission is approximately 1.8%. To minimize the risk of blood-borne pathogen transmission from HCWs to patients, all HCWs should adhere to standard precautions, including the appropriate use of hand washing, protective barriers, and care in the use and disposal of needles and other sharp instruments. Employers should have in place a system that includes written protocols for prompt reporting, evaluation, counseling, treatment, and follow-up of occupational exposures that may place a worker at risk of blood-borne pathogen infection. A sustained commitment to the occupational health of all HCWs will ensure maximum protection for HCWs and patients and the availability of optimal medical care for all who need it.

Genoepidemiology and pathogenicity of hepatitis G virus in Japan

A recently discovered non-A non-B hepatitis virus has been designated hepatitis G virus (HGV). Blood contamination has been proposed as its mode of transmission. We studied the genoprevalence of HGV in Japanese people at high risk. HGV was identified in serum by a reverse-transcription polymerase chain reaction. HGV was detected in 16.0% of intravenous drug users (IDUs) (n = 25), 16.2% of those with tattoos (n = 37), 10.9% of IDUs with tattoos (n = 55), 5.7% of chronic hepatitis (CH)-C patients (n = 87), and in none of the CH-B (n = 50) or CH non-B non-C (n = 46) patients. Serum alanine aminotransferase (ALT) levels of those infected with HGV alone (n = 3) were all within normal range. In the patients with CH-C, serum ALT levels of those coinfected with HGV were similar to serum ALT levels of those without HGV infection. A phylogenetic tree of isolated HGV clones showed that the HGVs of these subjects bore only a distant-resemblance to clones reported from Africa and North America, and that variation in the phylogenetic index of HGV clones was small. These results suggest that HGV clones from different areas have genetic heterogeneity and that HGV causes no or mild hepatitis.

Colourimetric point mutation assay: for detection of precore mutants of hepatitis B

A colourimetric assay for the analysis of point mutations in PCR amplified DNA fragments from hepatitis B virus (HBV) is described. The method was applied for analysis of the single point mutation in codon 28 of the precore gene of HBV, which inhibits expression of HBe antigen. The assay, which uses a microtitre plate formate, incorporates fluorescein-labelled dideoxynucleotides as opposed to radioactively-labelled deoxynucleotides used in methods described previously. Synthetic control wild type and mutant oligonucleotides were tested to optimise the reaction conditions. The assay was thus shown to yield both qualitative and quantitative data on the relative proportions of wild type and mutant sequences within a given sample. Amplicons from clinical specimens of known sequence were analysed to validate the assay. Sixteen chronic carriers of HBV were tested using the codon 28 point mutation assay, and the results were confirmed by direct sequencing. The method described is suitable for applications where point mutations are of interest.