Detection of hepatitis B virus polymerase variations resistant to lamivudine therapy

Objective To investigate variations in hepatitis B virus (HBV) polymerase g ene in chronic HBV infected patients resistant to lamivudine therapy. Methods Specimens were obtained from nine patients with chronic HBV infecti on, who were resistant to lamivudine therapy. Partial segments of the HBV D NA polymerase gene were amplified by polymerase chain reaction (PCR). Nucle otide sequence was performed using an applied 373 automated sequencer. Titr e of HBV DNA was measured by branched-DNA assay (Chiron). Results 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 o f the HBV polymerase, three of those were substitutions of isoleucine for m ethionine (M), and two were substitutions of valine(V) for methionine. Addi tionally, 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 lit eratures. With respect to viremia, in two subjects with low titre of HBV DN A (< 100 MEq/ml), no variation was found in the YMDD motif, whereas in seve n patients with high titre of HBV DBA (> 300 MEq/ml), five (71%) had variat ions in the YMDD motif. Conclusions Lamivudine is a potent anti-viral agent for treatment of chroni c HBV infection. Resistance to lamivudine is likely caused by the variation s in the YMDD motif of the HBV polymerase gene.