Detection of predominant YMDD mutants at the stage of viral DNA negativity for the prognosis of viral DNA breakthrough.

Abstract

YMDD mutants with or without compensatory mutations are found in chronic hepatitis B patients showing the phenotypic resistance during lamivudine therapy. But it is uncertain that the detection of YMDD mutation is absolutely associated with accompanying HBV viral DNA breakthrough. In the present study we determined if predominant presence of YMDD mutants at the stage of viral DNA negativity could be prognosis marker for occurrence of viral DNA breakthrough. We retrospectively analyzed YMDD genotypes in 740 consecutive samples collected from 116 patients throughout lamivudine treatment using a matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS)-based genotyping assay, termed Restriction Fragment Mass Polymorphism (RFMP). The RFMP exploits differences in molecular masses between wild type and variant bases of rtM204V/I. The capacity of the RFMP assay to show relative abundance among viral species enables us to monitor YMDD genotype dynamics in the longitudinal samples more effectively. The result demonstrated that YMDD mutants can be present throughout a course of lamivudine therapy irrespective of occurrence of viral DNA breakthrough, indicating that a mere detection of YMDD mutants could not always predict the viral DNA breakthrough. When mutant predominance was defined by 5-times higher amount of mutant compared to wild type, a significantly stronger association could be found between detection of YMDD mutant predominance and the following viral DNA breakthrough event. In conclusion our study showed that detection of predominant YMDD mutants rather than of mutant presence has a more prognostic value for viral DNA breakthrough. A close and periodical testing should be useful to detect predominant YMDD mutants for monitoring drug resistance as it develops, enabling early intervention and prevention.