A mutation of the start codon in the X region of hepatitis B virus DNA in a patient with non-B, non-C chronic hepatitis

In silico analysis of mutations associated with occult hepatitis B virus (HBV) infection in South Africa

Occult hepatitis B virus (OBI) infection is defined by the presence of viral DNA in the liver and/or serum in absence of hepatitis B surface antigen (HBsAg). While multiple studies have identified mutations that are associated with OBI, only a small portion of these mutations have been functionally characterized in vitro. Using complementary in silico approaches, the effects of OBI-associated amino acid mutations on HBV protein function in HBV/HIV-positive ART-naïve South Africans were evaluated. Two OBI-associated mutations in the PreS1 region, one in the PreS2 region, and seven in the surface region of subgenotype A1 sequences were identified as deleterious. In subgenotype A2 sequences, 11 OBI-associated mutations in the PreS1 region, seven in the PreS2 region, and 31 in the surface region were identified as deleterious. In the polymerase region, 14 OBI-associated mutations in subgenotype A1 and 71 OBI-associated mutations in subgenotype A2 were identified as deleterious. This study utilized in silico approaches to characterize the likely impact of OBI-associated mutations on viral function, thereby identifying and prioritizing candidates and reducing the significant cost associated with functional studies that are essential for mechanistic studies of the OBI phenotype.

Molecular mechanisms underlying HBsAg negativity in occult HBV infection

Although genomic detection is considered the gold standard test on HBV infection identification, the HBsAg investigation is still the most frequent clinical laboratory request to diagnose HBV infection in activity. However, the non-detection of HBsAg in the bloodstream of chronic or acutely infected individuals has been a phenomenon often observed in clinical practice, despite the high sensitivity and specificity of screening assays standardized commercially and adopted in routine. The expansion of knowledge about the hepatitis B virus biology (replication/life cycle, genetic variability/mutability/heterogeneity), their biochemical and immunological properties (antigenicity and immunogenicity), in turn, has allowed to elucidate some mechanisms that may explain the occurrence of this phenomenon. Therefore, the negativity for HBsAg during the acute or chronic infection course may become a fragile or at least questionable result. This manuscript discusses some mechanisms that could explain the negativity for HBsAg in a serological profile of individuals with HBV infection in activity, or factors that could compromise its detection in the bloodstream during HBV infection.

Mutations associated with occult hepatitis B in HIV-positive South Africans

Occult hepatitis B is characterized by the absence of hepatitis B surface antigen (HBsAg) but the presence of HBV DNA. Because diagnosis of hepatitis B virus (HBV) typically includes HBsAg detection, occult HBV remains largely undiagnosed. Occult HBV is associated with increased risk of hepatocellular carcinoma, reactivation to chronic HBV during immune suppression, and transmission during blood transfusion and liver transplant. The mechanisms leading to occult HBV infection are unclear, although viral mutations are likely a significant factor. In this study, sera from 394 HIV-positive South Africans were tested for HBV DNA and HBsAg. For patients with detectable HBV DNA, the overlapping surface and polymerase open reading frames (ORFs) were sequenced. Occult-associated mutations-those mutations found exclusively in individuals with occult HBV infection but not in individuals with chronic HBV infection from the same cohort or GenBank references-were identified. Ninety patients (22.8%) had detectable HBV DNA. Of these, 37 had detectable HBsAg, while 53 lacked detectable surface antigen. The surface and polymerase ORFs were cloned successfully for 19 patients with chronic HBV and 30 patients with occult HBV. In total, 235 occult-associated mutations were identified. Ten occult-associated mutations were identified in more than one patient. Additionally, 15 amino acid positions had two distinct occult-associated mutations at the same residue. Occult-associated mutations were common and present in all regions of the surface and polymerase ORFs. Further study is underway to determine the effects of these mutations on viral replication and surface antigen expression in vitro.

Occult hepatitis B infection in the immigrant population of Sicily, Italy

In Italy, about 7 % of the resident population is represented by immigrants originating from geographic regions at high endemicity for hepatitis B virus infection. This study aims to assess the prevalence of occult HBV infection (OBI) including the identification of HBV-genotypes in a population of immigrants serologically negative for hepatitis B surface antigen (HBsAg). Between May 2006 and May 2010, 339 immigrants were tested for markers of HBV, hepatitis C virus (HCV) and human immunodeficiency virus (HIV) infections. HBV-DNA was tested by using nested-PCR assays on three different genetic region. HBV-DNA was detected in plasma samples of 11/339 (3.2 %) patients. Most of them had no serological markers of HBV infection, 3/58 (5.2 %) were anti-HBc-alone, and 4/13 (30.8 %) were anti-HIV positive. HIV positivity was the only factor independently associated with the higher probability of observing OBI (OR = 16.5, p < 0.001). No HCV co-infected patients were found. Genotype D was detected in 9/11 (81.8 %) OBI cases, while the remaining two (18.2 %) were classified as genotype E. Although OBI was found at lower rate than expected among immigrants from highly endemic countries, anti-HBc alone positivity was confirmed as a sentinel marker of occult HBV infection. Nevertheless, a marked heterogeneity of HBV markers was found among HBV-DNA positive subjects. Our finding evidenced the predominance of HBV-genotype D viral strains among OBI cases, also in those from geographical areas where overt HBV infections are mainly sustained by viral genotypes other than D.

Potential mutations associated with occult hepatitis B virus status

CONTEXT

Occult hepatitis B virus (HBV) status (OHBS) is simply defined as the presence of HBV DNA in the liver (with or without detectable HBV DNA in the serum), in the absence of serum HBV surface antigen (HBsAg). Importance of OHBS is mostly clinical, related to its possible role in spreading through blood transfusion and liver transplantation; causing classic forms of HBV. Mechanisms underlying this entity are poorly defined. Several possibilities have been suggested, with major classification into two groups: defective host immune response and viral replication activity through mutations of HBV DNA sequence. Mutations are extensively investigated in all four overlapping open reading frames (ORFs) of HBV genome, to define their possible role in the pathogenesis of OHBS. Some of these mutations like S-escape mutants could not be detected by the routine available assays, making them difficult to diagnosis. Therefore, trying to detect this covert condition could be more helpful for defining better preventive and therapeutic strategies.

EVIDENCE ACQUISITION

In the present study we provided an in-depth review of the most important new data available on different mutations in HBV genome of patients with OHBS, which may play a role in the pathogenesis of OHBS. The data were collected through reviewing the full-text articles, identified by the PubMed search, using the following keywords and their different combinations: occult hepatitis B, HBV genome, "a" determinant, HBV open reading frames, S mutations, X mutations, P mutations and C mutations.

RESULTS

Variants within the major hydrophilic region (MHR) of the HBsAg, deletions in the pre-S1region, codon stop in the S open reading frames (ORF), sporadic non common mutations, some mutations affecting the posttranslational production of HBV proteins in the S ORF like deletion mutations, mutations in start codon and nucleotide changes in the X ORF, deletion and point mutations in P ORF and sometimes, nucleotide substitution in the C ORF are among the assumed mutations detected to have a role in OHBS appearance.

CONCLUSIONS

Studies mostly lacked a control group and the whole-length HBV sequencing was scant with conflicting results, suggesting that OHBS is often a result of multiple mechanisms. Additional studies on full-length HBV genomes from occult and non-occult HBV cases may shed more light on the interplay between different mechanisms involved in the pathogenesis of OHBS.