Hepatitis B surface gene 145 mutant as a minor population in hepatitis B virus carriers

BACKGROUND: Hepatitis B virus (HBV) can have mutations that include the a determinant, which causes breakthrough infection. In particular, a single mutation at amino acid 145 of the surface protein (G145) is frequently reported in the failure of prophylactic treatment. The aim of this study was to evaluate the frequency of the a determinant mutants, especially the G145 variant, in Japan, where universal vaccination has not been adopted. METHODS: The present study was a retrospective study. The study cohorts were defined as follows: group 1, children with failure to prevent mother-to-child transmission despite immunoprophylaxis (n = 18, male/female = 8/10, age 1-14 years; median 6 years); group 2, HBV carriers who had not received vaccination or hepatitis B immunoglobulin (n = 107, male/female = 107, age 1-52 years; median 16 years). To detect the G145R and G145A mutants in patients, we designed 3 probes for real-time PCR. We also performed direct sequencing and cloning of PCR products. RESULTS: By mutant-specific real-time PCR, one subject (5.6%) was positive for the G145R mutant in group 1, while the G145 mutant was undetectable in group 2. The a determinant mutants were detected in one (5.6%) of the group 1 subjects and 10 (9.3%) of the group 2 subjects using direct sequencing, but direct sequencing did not reveal the G145 mutant as a predominant strain in the two groups. However, the subject who was positive according to the mutant-specific real-time PCR in group 1 had overlapped peaks at nt 587 in the electropherogram. In group 2, 11 patients had overlapped peaks at nt 587 in the electropherogram. Cloning of PCR products allowed detection of the G145R mutant as a minor strain in 7 (group 1: 1 subject, group 2: 6 subjects) of 12 subjects who had overlapped peaks at nt 587 in the electropherogram. CONCLUSIONS: The frequency of the a determinant mutants was not high in Japan. However, the G145R mutant was often present as a minor population in children and adults. HBV carriers might have the a determinant mutants as a minor form.