Influential Factors Of HBV Gene Mutation Rate Mother-child Patients With Chronic HBV Infection

Background Chronic infection with hepatitis B virus(HBV) is a global public health issues that threat human health. There were 93 million HBV patients in China, accounting for about 1/3 of the world’s HBV patients. Among DNA viruses, HBV is highly prone to mutations during evolution because of existing reverse transcription and lacking proof-reading repair-enzyme activity of reverse transcriptase. The mutation of HBV is between DNA virus and RNA virus. In the previous studies on HBV mutation rate,the conclusion were from 1.4×10-5 to 2.38×10-4 substitution/site/year. The related factors of the huge difference of HBV mutation were not yet defined. In the sutdy, we selected six pairs of mother-child patients with chronic HBV infection as the research objects. Amplified full-length HBV by PCR from sera samples and analyzed the nucleotide substitution rate as well as the relevance of their disease processes.Methods A total of six pairs of mother-child patients with chronic HBV infection who received treatment at our hospital Outpatient or Inpatient Department from June 2014 to December 2014 were enrolled this study. Full-length HBV by PCR from sera samples were amplified and the nucleotide substitution rate as well as the relevance of their disease processes were analyzed. Using automatic biochemical analyzer, measure the levels of serum ALT/AST, using enzyme-linked immunoassay(ELISA), qualitative detection of hepatitis b five, fluorescence quantitative PCR method to detect the levels of serum HBV DNA. To investigate the characteristics of the mutation in different hosts and its potential correlation with different immunephases.Results 1. Six pairs of mother-child patients were HBV B genotype. In the detection of HBV serological markers, the HBe Ag of the child of family 3 is negative, nevertheless the others is positive. The son of family 1 and the daughters of family 2 had increased ALT/AST, while the others were normal. All the patients are CHB or ASC. 2. Phylogenetic tree was built by the PCR sequences. The full-length HBV sequences of six pairs of mother-child patients were analyzed with the standard sequence, like A(X02763), B(GQ205440), C(GQ205441), D(X02496). Through the phylogenetic tree, highly homologous nucleotide sequences were closed. The family members were closer than others, and the standard sequence of genotype B was closer with these patients than other standard sequences. 3.The nucleotide substitution rates were 6.67×10-5, 2.83×10-5, 2.33×10-5, 1.48×10-4, 1.83×10-4, 1.24×10-4 substitution/site/year and the differences could be up to 7.85 times, in which the HBV nucleotide substitution rates within pedigrees were 2.36 and 6.35 times. The HBV nucleotide substitution rates of immune tolerance phase were 2.83×10-5and 1.24×10-4 substitution/site/year, while the rates of the non-immune tolerant phase were 2.33×10-5 to 1.83×10-4 substitution/site/year. The nucleotide substitution rate in each coding region was different, but did not reach the statistical significant(Nucleotide: χ2=2.812, p=0.422; Amino acids: χ2=2.344,p=0.504).Conclusions The nucleotide substitution rates of full-length HBV of different patients are quite different which may be associated with the natural course of HBV infection, absence, in addition to considering virus itself.