Objective: To invistigate the characteristics of mutations in EnhII/CP/PreC of HBV in AsC children infected through mother-to-infant transmission and their AsC mothers with different degrees of viremia.Methods: There were 15 pairs of children and mothers.They were divided into three groups based on the level of viremia: groupⅠ(both children and mothers presented high viremia)

groupⅡ(children presented high and mothers presented low viremia) and groupⅢ(children presented low and mothers were high viremia).There were 5 pairs in each group with 4/5 of HBV being B/adw2 and 1/5 of HBV being C/adrq+ in each group.EnhII/CP/PreC was amplified and cloned into pGEM-T vector.Tow clones were selected to sequence each patient.Results: Substitution was the main model of mutations.There were no significant differences in the mutation numbers in EnhII/CP/PreC among high viremia groups or between two low viremia groups.There were significant differences between each high viremia group and each low viremia group.In patients with high viremia

there were 6 mutational positions in 32 clones in 16/20 patients with B/adw2

and there were 4 mutational positions in 8 clones in 4/20 patients with C/adrq+.In patients with low viremia(mothers of group Ⅱ and children of group Ⅲ)

there were 26 mutational positions totally.Conclusion: The mutations in EnhII/CP/PreC are related to the degree of viremia in AsC children infected through mother-to-infant transmission and their AsC mothers

and no associated with age.