The diagnostic and clinical impact of the genetic variability of the S (surface) gene of hepatitis B virus / Diagnostische und klinische Relevanz der genetischen Variabilität des S- (surface) Gens des Hepatitis B Virus

Abstract

Abstract The genetic variability of hepatitis B virus (HBV) represents a challenge for the sensitivity of immunodiagnosis, especially for the detection of surface antigen (HBsAg). There are two types of variants of HBV. Naturally occurring variants are the results of random changes selected over years of population pressure. These variants include HBV genotypes and unusual sequences, which may be poorly detected by immunoassays. The selected variants are mutants that arise in individuals under medically (vaccine, hepatitis B immune globulin and antiviral therapy) or naturally (chronic hepatitis B) induced immune pressure. HBV S-gene mutants have been identified in successfully immunized people worldwide. Based on the assumption that current vaccines containing S protein do not cross-protect against S gene mutants, a mathematical model predicts the disappearance of wild-type HBV in areas with HBsAg endemicity and the emergence of S gene mutants in approximately 100 years as a consequence of universal HBV vaccination. Mutant viruses may escape detection by commercial HBsAg kits. There are several reports on HBsAg negative carriers (HBV-DNA positive) of S gene mutants with immunosilent infection or "unusual" serologic constellations. Although S gene mutants have been found to be associated with a more severe clinical course of HBV infection and hepatocellular carcinoma, the clinical significance of the genetic variability of HBV genotypes and HBsAg mutants needs to be further investigated. Detection of HBsAg needs to be improved by the introduction of new HBsAg assays able to recognize S gene mutants described so far and with a lower detection threshold than current immunoassays in order to detect smallest amounts of HBsAg in low-level carriers. There is also a need for more complete epidemiological data on the prevalence of HBsAg mutants in Western Europe and assays for the (differential) screening of mutants need to be developed and evaluated.