[Hepatitis B virus gene mutations in the sera of three patients with coexisting hepatitis B surface antigen and anti-surface antibody].
We analyzed gene mutations in the Hepatitis B virus of three virus carriers with coexisting Hepatitis B surface(HBs) antigen and anti-HBs antibody. Viral DNAs were extracted from sera and the pre-S, S and X(including core promoter and pre-core region) regions were amplified by PCR, and sequenced. Case 1 and Case 2 were positive for HBe antigen, while Case 3 was negative. All three cases were positive for HBe antibody and HBV DNA. In the S gene region, various point mutations were detected in all three cases. Mutations were clustered in the first hydrophilic loop region(codon 47-46) essential for the secretion of surface antigen. A few mutations were detected in 'a' loop(codon 124-147) of the S gene. None of the cases had an amino acid substitution of codon 145 of the S gene that is reported to be responsible for weak recognition by the HBs antibody. These data suggest the existence of hyper-variable sequence in S region, or otherwise result of low-fidelity of Taq DNA polymerase-reaction. Case 1 possessed a point mutation, T to C at nucleotide position 1753, in the region overlapping the coding region of the X gene and the CCAAT/enhancer binding protein(C/EBP) binding region within the core promoter region. Case 2 possessed both a large deletion(129 bp) in the pre-S1 and in-frame deletions of 15 and 27 bp in the pre-S2 region. Case 3 had an in-frame deletion of 30 bp in the pre-S2 region, and a point mutation in precore region. The point mutation, G to A at a nucleotide position 1986, converts Trp(TGG) to a stop codon TAG, and may contribute the fulminant hepatitis. These results suggest that the mutations in the pre-S, the core promoter, or the X gene may imply coexistence of the HBs antigen and antibody after seroconversion, while the point mutations in the S region are not likely to be responsible for the HBV escape mutant.