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Functional analysis of a rare HBV deletion mutant in chronically infected children
Patrick Gerner1, Heike Marie Clara Schäfer, Reinhild Prange
1Children's Hospital, Helios Klini Kum, Wuppertal, Heusnerstrasse 40, D-42283 Wuppertal, Germany.
Insights
Hepatitis B virus (HBV) preS deletion mutants are rare in children. However, one case suggests these mutants may worsen liver inflammation and damage during chronic HBV infection.
Area of Science:
- Hepatology
- Virology
- Pediatric Infectious Diseases
Background:
- Chronic hepatitis B virus (HBV) infection can lead to liver damage.
- Deleted HBV preS mutants may enhance liver damage through viral protein accumulation and cell death.
- The prevalence and impact of these mutants in children remain largely unstudied.
Purpose of the Study:
- To investigate the prevalence of HBV preS deletion mutants in children.
- To determine the clinical impact of these mutants on liver inflammation.
- To elucidate the in vitro replication and packaging characteristics of preS deletion mutants.
Main Methods:
- PCR and direct sequencing of the preS region in serum samples from 60 children.
- 10-year longitudinal follow-up of a child with a preS deletion mutant.
- In vitro transfection and replication assays using human hepatoma cells.
Main Results:
- Only one child (1.5%) showed a mixed HBV population with a preS deletion mutant.
- The identified mutant altered the large surface protein and small surface promoter.
- In vitro studies demonstrated impaired nucleocapsid packaging by the mutant.
- Clinical follow-up showed increased liver enzymes despite seroconversion in the affected child.
Conclusions:
- HBV preS deletion mutants are uncommon in childhood infections.
- Functional and clinical data from one case suggest potential for increased liver inflammation.
- Further studies with larger cohorts are needed to confirm the impact of these mutants in pediatric HBV.
Abstract:
Liver damage caused by chronic hepatitis B virus (HBV) infection may be enhanced through the selection of deleted HBV preS mutants by intracellular accumulation of viral proteins and subsequent cell death. However, the prevalence and impact of such mutants on the clinical course of infection have not yet been studied in children. Serum samples from 60 children (mean age 9.8 y) were investigated by means of PCR and direct sequencing of the entire preS region. Only one patient (1.5%) was found with a mixed HBV population of a deletion spanning 183 nucleotides and wild-type sequences. This mutation alters the HBV large-surface protein and removes the small-surface promoter. To clarify the significance of this mutation, we studied 14 serial serum samples of the child within a follow-up of 10 y. After occurrence of the mutation, the liver enzymes increased, despite seroconversion to anti-HBe. Transfection of an HBV expression construct containing this deletion into human hepatoma cells by using an HBV in vitro replication system showed that the mutant lost the ability of nucleocapsid packaging as a result of alteration of the transmembrane topology of the large surface protein. This effect could not be restored by coexpression of wild-type large- or small-surface proteins in trans. In conclusion, the circulation of HBV preS deletion mutants is rare in childhood. However, our functional and clinical follow-up studies in one child suggest that such a mutant may have the potential to aggravate liver inflammation, especially if corroborated with larger numbers of children.