To investigate the genovariation of HBV S gene on failure of mother-to-child transmission blocking in Yunnan Province.

A total of 26 pairs of HBsAg-positive perinatal mothers and their newborns who confirmed failure of prevention of mother to child transmission (PMTCT) were randomly selected from January to June, 2011 in Yunnan. Their serum samples were collected for HBV DNA detection and gene sequencing. The further research was performed for the variation points of "a" antigenic determinant of HBV S gene in both mother group and infant group.

Of the 26 pairs of mother and infant samples who were failure of PMTCT, 9 pairs(34.62%) belonged to C genotype, and 11(42.31%) to B genotype. The rest 6 pairs(23.08%) had genetic mutations, in which 2 pairs had mutations of gene subtype belonged to C gene and 4 pairs had variations of genotype from mother to infant. There were 7 variation points in "a" antigenic determinant of HBV S gene, including T126I, T131N, M133L, F134Y, T140I,T143S and D144A. Double point mutation was the most frequent mutation in both mother(14 samples) and infant group (11 samples) . 126I/T143S point mutations of C3 genotype had the highest mutation rate. The average HBV DNA levels were>2×10⁵ IU/mL in both mother group and infant group. The mutation rates in "a" antigenic determinant of HBV S gene were 56.75% (21/37) , 60.00% (3/5) and 100.00% (10/10) in high (>2×10⁵ IU/mL) , middle(500-2×10⁵ IU/mL) and low (<500 IU/mL) HBV DNA level group, respectively.

In these cases with failure of PMTCT, the factor of genovariation is not dominant but should not be ignored in Yunnan. The points of mutation in "a" antigenic determinant of HBV S gene are dispersed, and have not yet been formed advantage mutants. It should be strengthen the monitoring in order to prevent the spread of the mutant strains.

Hepatitis B; Preventing mother-to-infant transmission; Genovariation; Amino acid sequence