BACKGROUND: There is an increasing need for the early detection of emerging mutations in the tyrosine-methionine-aspartate-aspartate (YMDD) motif of hepatitis B virus (HBV) DNA polymerase with using sensitive molecular methods. METHODS: We evaluated the usefulness of monitoring lamivudine resistance using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based assay (the restriction fragment mass polymorphism; RFMP) in comparison with the direct sequencing assay, the TRUGENE ' HBV genotyping kit. We also investigated the treatment responses in relation to the presence of YMDD mutants. The sera from 50 chronic HBVs patients were analysed for the presence of YMDD mutants by performing RFMP and TRUGENE. The results at codons 180 and 204 were compared for 46 patients. RESULTS: The concordance rate between the two assays was 65.2% (30/46). All the discordance corresponded to the detection of additional virus populations by RFMP. Early detection of mutants before viral breakthrough was accomplished by RFMP in two patients. Persistence of very low viraemia was observed in five patients who harboured mutant virus populations. Additional information was provided by TRUGENE in eight patients. CONCLUSIONS: RFMP showed a superior ability for detecting minor mutant virus populations compared with TRUGENE. However, the results of highly sensitive RFMP should be interpreted carefully because lamivudine could be effective despite the presence of mutants. RFMP could be a practical tool in conjunction with regular measurements of the HBV viral load for the early detection of lamivudine resistance and the timely introduction of new antiviral drugs.
BACKGROUND: There is an increasing need for the early detection of emerging mutations in the tyrosine-methionine-aspartate-aspartate (YMDD) motif of hepatitis B virus (HBV) DNA polymerase with using sensitive molecular methods. METHODS: We evaluated the usefulness of monitoring lamivudine resistance using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based assay (the restriction fragment mass polymorphism; RFMP) in comparison with the direct sequencing assay, the TRUGENE ' HBV genotyping kit. We also investigated the treatment responses in relation to the presence of YMDD mutants. The sera from 50 chronic HBVs patients were analysed for the presence of YMDD mutants by performing RFMP and TRUGENE. The results at codons 180 and 204 were compared for 46 patients. RESULTS: The concordance rate between the two assays was 65.2% (30/46). All the discordance corresponded to the detection of additional virus populations by RFMP. Early detection of mutants before viral breakthrough was accomplished by RFMP in two patients. Persistence of very low viraemia was observed in five patients who harboured mutant virus populations. Additional information was provided by TRUGENE in eight patients. CONCLUSIONS:RFMP showed a superior ability for detecting minor mutant virus populations compared with TRUGENE. However, the results of highly sensitive RFMP should be interpreted carefully because lamivudine could be effective despite the presence of mutants. RFMP could be a practical tool in conjunction with regular measurements of the HBV viral load for the early detection of lamivudine resistance and the timely introduction of new antiviral drugs.