Clinical characteristics of asymptomatic hepatitis B virus carriers with YMDD mutant not treated with lamivudine.

We previously developed a method of detecting drug-resistant mutation of hepatitis B virus (tyrosine (Y)-methionine (M)-aspartic acid (D)-aspartic acid (D) (YMDD) mutation) caused by the antiviral agent lamivudine. Using this method, we also reported that YMDD mutation is present in asymptomatic carriers that had not been administered antiviral agents. Thus, we investigated the clinical characteristics of 18 asymptomatic carriers of hepatitis B virus by various biochemical and virological examinations, and compared the results between five subjects with YMDD mutation and 13 subjects without mutation. Although there was no significant difference in the results of various examinations between the two groups, the quantity of virus was generally small, and S-antigen disappeared in 2 patients in whom YMDD mutation was detected. These results suggest that there is no particular cause for the appearance of mutant viruses, but that they occur spontaneously as they gain fitness and, with a subsequent decrease in the absolute quantity of viruses, become relatively easy to detect.