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Objective: To explore the point mutation in hepatitis B virus polymerase (HBV P) gene in HBV-infected patients resistant to lamivudine., Methods: HBV P gene was amplified by PCR and the products was sequenced to analyze the YMDD mutation. Then the variants were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) with the following restriction enzymes: Fok I, Ssp I, Alw441 and were separated by 8.0% polyacrylamide gel electrophoresis., Results: Comparing with the sequences of standard HBV genome, there were 16 patients with G743C mutation and 1 patient with G743A mutation, and the codon ATG turned to ATC and ATA, YMDD motif changed into YIDD. But this kind of YIDD mutation was not proved by PCR-RFLP assay in the 17 patients., Conclusions: The G743C and G743A mutations in HBV P gene, resulting in YMDD motif changed into YIDD, are detected only by direct sequencing, not by PCR-RFLP. The new kind of G743C and G743A point mutations in HBV P gene is important for the detection of HBV P gene YMDD mutation.

Objective: To study the types and emergence time of YMDD motif mutation in hepatitis B virus (HBV) polymerase gene during lamivudine treatment., Methods: The serum samples were collected from 33 patients with HBV DNA rebounding and 2 non-responders after at least one year lamivudine treatment. HBV polymerase gene was amplificated by PCR, then the products were detected by restriction fragment length polymorphism (RFLP) and by direct sequence analysis., Results: The variants with YMDD mutation were 14 out of the 35 patients. Mutation patterns detected in these patients included four YIDD, six YVDD, three YI/VDD and one YI/MDD. The mean emergence time of YMDD variants was 11.07+/-3.65 months after the treatment, and the earliest one and the latest one occurred 5 months and 17 months after the treatment respectively. The emergence times of YIDD, YVDD, YI/VDD were (10.00 +/- 1.41) months, (11.67 +/- 4.41) months and (13.33 +/- 3.31) months respectively, which had no statistical significance (F = 0.543, P < 0.05). Three patients treated with lamivudine 200 mg every day after the mutation were followed up for 6 months, whose HBV variants had not vanished., Conclusions: There are many kinds of HBV variants after lamivudine treatment, including YIDD, YVDD, YI/VDD and YI/MDD. The emergence time of variants is quite variable between different types and the mean time is (11.07 +/- 3.65) months after treatment, and there is no relationship between the type of YMDD mutation and the time of lamivudine administration.