Objective   To investigate the relationship between HBV intrauterine transmission and gene variation by analysis of HBV PreS/S gene sequence in intrauterine transmission.

  Methods   According to whether neonate was infected by HBV in uterus, their HBsAg positive mothers were divided into intrauterine infection group and non-intrauterine infection group.PreS/S gene nt2848-835 of HBV was amplified by polymerase chain reaction(PCR), then the PCR products were cloned and sequenced.The sequences were compared with each other between groups.

  Results   All HBV sequences were genotype C and subtype adr.The nucleotide similarity were 99.2%-100% between the mother and her neonates.In every case, there were several mutations in preS1, preS2, and S regions, respectively.Almost no significant mutation was found in "a" determinant of S gene.The mutation rate positions nt2909, nt399, nt293 and nt483 in non-intrauterine infection group was higher than that of intrauterine infection group.The mutation rates in preS2, S, and preS/S region were also higher in non-intrauterine infection group.

  Conclusion   The preS/S gene heterogeneity of HBV strains which can infect neonate in uterus was lower.The results suggest that the strains of HBV with lower mutation rate in PreS/ S gene can cause intrauterine infection easily.