Detection of hepatitis B virus polymerase variations resistant to lamivudine therapy

To investigate variations in hepatitis B virus (HBV) polymerase gene in chronic HBV infected patients resistant to lamivudine therapy. Specimens were obtained from nine patients with chronic HBV infection, who were resistant to lamivudine therapy. Partial segments of the HBV DNA polymerase gene were amplified by polymerase chain reaction (PCR). Nucleotide sequence was performed using an applied 373 automated sequencer. Titre of HBV DNA was measured by branched-DNA assay (Chiron). Of nine patients with HBV DNA positive after 64 weeks of treatment, five (56%) had variations in the highly conserved YMDD motif in domain C of the HBV polymerase, three of those were substitutions of isoleucine for methionine (M), and two were substitutions of valine(V) for methionine. Additionally, in two patients with variations characterized by substitutions of V for M, one had a simultaneous amino acid change from the first aspartic acid to glycine and this pattern of variation was not reported in other literatures. With respect to virernia, in two subjects with low titre of HBV DNA (< 100 MEq/ml), no variation was found in the YMDD motif, whereas in seven patients with high titre of HBV DBA (> 300 MEq/ml), five (71%) had variations in the YMDD motif. Lamivudine is a potent anti-viral agent for treatment of chronic HBV infection. Resistance to lamivudine is likely caused by the variations in the YMDD motif of the HBV polymerase gene.