Variation in the core and X genes of hepatitis B virus

Variation in viral genomes is dependent upon rates of polymerase error and the relative influence of selection pressures. For HBV, it appears that there is substantial immune pressure in keeping with the immunopathogenesis; the ability of the virus to persist is probably linked with this process. As the viral genome is small, mutants may have multiple effects, particularly apparent within regions that have overlapping functions, such as the encapsidation signal and the X gene. Here, an attempt has been made to correlate variation within the pre-core/core gene with clinical progression and response to interferon and to put forward hypotheses to show the relationship of these mutations to the immune response. Their effects on overlapping regions are also discussed. Little is currently known about the functional importance of mutations within and around the X gene, but it is likely that this will prove a fruitful area of research.