A novel stop codon mutation in HBsAg gene identified in a hepatitis B virus strain associated with cryptogenic cirrhosis.
OBJECTIVE
HBsAg is the most important serological marker for acute or chronic hepatitis B. Nevertheless, there were reports of HBsAg-negative infection caused by hepatitis B virus in recent years. We had a patient with crytogenic cirrhosis who was negative for HBsAg, positive for anti-HBs and HBeAg. This paper was to explore the pathogenic and molecular basis of the unusual serological pattern.


METHODS
HBV serologic markers were qualitatively and quantitatively determined. HBV DNA in serum was qualitatively tested using routine Polymerase chain reaction(PCR), and the viral level was determined with real-time fluorescence quantitative PCR. HBsAg gene was amplified and cloned. Four clones were sequenced. The new genomic sequences were compared with GenBank on the DNA level as well as the protein level.


RESULTS
The qualitative results of serological markers were HBsAg(-), anti-HBs(+), HBeAg(+), anti-HBe(-) and anti-HBc(+). The quantitative results of serological marker were HBsAg (S/N): 0.77 (cut off of S/N: >=2.00), HBeAg (S/N): 56.43 (cut off S/N: >=2.10), anti-HBc (S/C(0)): 2.03 (cut off of S/C(0): <=1.00). The viral level was as high as 1.54 x 10(9) copies/ml. Sequencing of the HBsAg gene clones revealed a unique point mutation at nucleotide 336 (C to A), which resulted in a novel stop codon at aa 61. The novel HBsAg gene stop mutation had not been described.


CONCLUSIONS
The lack of detection of HBsAg in the presence of high viral levels of replication may be caused by the existence of viral genomes harboring point mutations which resulted in stop codon upstream of the "a" determinant in HBsAg gene.
Yang
Xu
X
Liver Disease Research Center, The Second Xiangya Hospital, Central South University, 86 Ren Min Avenue, Changsha 410011, Hunan Province, China. yangxu@vip.163.com
Tang
Xiao-Peng
XP
Lei
Jian-Hua
JH
Luo
Hong-Yu
HY
Zhang
Yong-Hong
YH
D000595:Amino Acid Sequence; D001483:Base Sequence; D018388:Codon, Terminator / Q000235:genetics*; D006514:Hepatitis B Surface Antigens / Q000235:genetics*; D006515:Hepatitis B virus / Q000235:genetics*; D019694:Hepatitis B, Chronic / Q000821:virology*; D006521:Hepatitis, Chronic / Q000821:virology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D017354:Point Mutation
D018388:Codon, Terminator; D006514:Hepatitis B Surface Antigens