Viral mutant discovery in hepatitis B virus quasi-species in patients undergoing long-term lamivudine treatment.

result, it has a much higher error rate than DNA viral transcriptases, as it replicates through a RNA intermediate. HBV DNA is thus often present in quasi-species in an individual. One or more species may be favourably selected by factors such as host immune clearance and use of antiviral drugs.1 HBV variation plays an important role in HBV genotypes and drug-resistant mutations. It is clinically important to detect known and unknown mutations that are associated with or conferred by drug resistance.2 Current methods are insufficient to detect minor proportions of unknown mutants in an economic and efficient way. The most widely used method to detect novel mutants is direct sequencing. This provides complete sequence information, but it is not sufficiently sensitive for minor mutants present at <20% of the entire HBV population. Cloning and sequencing of virus sequences can also be used to detect minor mutations in HBV quasi-species, but it is costly, time-consuming, and labour-intensive.3 Thus, a high-throughput method for detecting virus mutations at minor proportions is needed. Matrixassisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) enables high accuracy, sensitivity and specificity. Some research groups have developed specific and sensitive assays based on this technology to detect known mutations.4,5 This study evaluated the performance of basespecific RNA cleavage and MALDI-TOF MS in HBV from chronic hepatitis B (CHB) patients undergoing long-term lamivudine treatment.