OBJECTIVETo identify factors associated with YMDD mutation in patients with chronic hepatitis B before and after lamivudine treatment in Zunyi region.

METHODS53 patients with chronic hepatitis B were enrolled in this study, HBV DNA,HBV markers, ALT, AST, TBil, albumin in the serum were examined at 0, 3, 6, 12, 18 and 24 months after lamivudine treatment. HBV genotype and YMDD mutation were determined by sequencing before lamivudine treatment. YMDD mutation was checked again if serum HBV DNA rebound to more than 1 x 10(4) copies/ml after the initial decrease.

RESULTSHBV genotype in Zunyi region is constitute of B, C and B+C genotype. YMDD mutation occurred in 18 cases after lamivudine treatment, the rate of YMDD mutation was 15.1%, and 34.0% after 1 year and 2 years treatment. There are four types of mutation: rtL180M/M204V, rtL180M/M204I, rtM204I, rtL180M. rtM204V mutation in C gene was always accompanied by rtL180M mutation (100%). The rate of rtL180M/M204V mutation in genotype C group was significantly higher than that in genotype B group (77.8% to 25.0%), the same was true for the rtL180M/ M204I mutation (22.2% to 12.5%). There was no point mutation in genotype C group. The point mutation of rtM204I and rtL180M appeared only in genotype B group. Gender, nation, family history of hepatitis B and HBeAg were not associated with YMDD mutation (P more than 0.05), while the mutation rate was associated with the disease course and severity of disease. YMDD mutation did not occur in patients with low HBV DNA level (less than 10(5) copies/ml).

CONCLUSIONYMDD mutation after lamivudine therapy is associated with HBV genotype and P gene mutation type, and prolonged treatment increases the the mutation rate. In order to reduce the incidence of YMDD mutation, patients with shorter disease course, lower HBV DNA level, more serious liver damage should be treated with lamivudine.