Sequence analysis of the S gene region in HBV DNA from patients positive for both HBsAg and HBsAb tests.
OBJECTIVE
To study the characteristics of mutation in the amino acids coded by the S gene region in the HBV DNA sequence and to comprehensively explore and analyze the cause of the double positive result phenomena in both HBsAg and HBsAb tests.


METHODS
Specimens collected from 43 cases of chronic hepatitis B patients with positive results for both HBsAg and HBsAb tests were used as the experimental group; specimens collected from 43 cases randomly picked from all patients with chronic hepatitis B with a single positive result for HBsAg test were used as the control group. In HBV DNA, the S gene region was amplified and sequenced. Amino acid sequences were grouped, and mutations were analyzed based on the sequencing results.


RESULTS
The patients were infected with HBV of the genotype B and C and those who with genotype C show more mutations than genotype B carriers. Compared with the control group, the experimental group had a marked increase in S gene amino acid mutations; a higher amino acid mutation rate was observed in the first loop (aa124-137) of the a-determinant (aa124-147) and there was a statistical difference (genotype B: 2.68% vs. 0.00%, P = 0.041; genotype C: 7.14% vs. 2.01%, P < 0.001).


CONCLUSIONS
The first loop in a-determinant of S gene sequence possesses a large numbers of mutated amino acids, leading to changes of antigenicity and simultaneous positive results in both HBsAg and HBsAb tests finally.
Clinical Laboratory, the Sixth People's Hospital, Affiliated to Shanghai Jiao Tong University, Shanghai, China.
Lei
L
Wang
Hua
H
Liu
Xiaoxiao
X
Ning
Feng
F
Gao