Abstract:

Objective To analyze relationship between genotypes and mutations in S gene sequence of chronic hepatitis B patients with positive results for both HBsAg and HBsAb tests (HBsAg+/HBsAb+). Methods Specimens collected from 43 cases of chronic hepatitis B patients with HBsAg+/HBsAb+ were used as experimental group, and specimens collected from 35 cases of newly diagnosed chronic hepatitis B patients with HBsAg+/HBsAb- were used as control group. The S gene region of HBV DNA was amplified and sequenced. The amino acid sequences were classified to different genotypes and the mutations were analyzed based on the sequencing results. Results The experimental group contained 8 patients of the B genotype and 35 patients of the C genotype, whereas the control group contained 9 patients of the B genotype and 26 patients of the C genotype. In experimental group, the average age of the C genotype patients [(50.2±16.3) years] was obviously older than that of the B genotype patients [(34.4±13.4) years](P=0.015). The mutation rates for the B and C genotypes in the experimental group were 0.77% and 1.64%, respectively (P=0.005). Whereas the mutation rates were 0.59% and 0.49% for the B and C genotypes in control group (P=0.597). In addition, among the C genotype patients, the experimental group had a marked increase in S gene amino acid mutations, and a higher amino acid mutation rate was observed in the major hydrophobic region (MHR, aa100~169), especially in the first loop (aa124~137) of α determinant (aa124~147). However, only few patients with the B genotype had mutations in α determinant. Conclusion The C genotype patients with HBsAg+/HBsAb+ are likely to have more mutations than the B genotype patients, especially the mutations in α determinant. The mutations in this area may lead to changes of antigenicity and simultaneous HBsAg+/HBsAb+ finally.

Key words: hepatitis B virus, HBsAg, HBsAb, genotype, mutation