Journal of Gastroenterology

, Volume 53, Issue 1, pp 18–26 | Cite as

Virological and Clinical Characteristics of Hepatitis B Virus Genotype A

  • Kiyoaki ItoEmail author
  • Masashi Yoneda
  • Kazumasa Sakamoto
  • Masashi Mizokami


Hepatitis B virus (HBV) infection is one of the most prevalent chronic viral infections in humans. The overall prevalence of hepatitis B surface antigen (HBsAg) is reported to be 3.6%; however, it varies depending upon the geographic area. HBV is classified into ten genotypes (A through J) on the basis of an intergroup genomic divergence of > 8%. Specifically, HBV genotype A exhibits several unique virological and clinical characteristics and can be further classified into seven subtypes. Among them, subtype A2 or Ae (A2/[e]) is occasionally responsible for nosocomial infection and among homosexual males. Regarding virological factors, the G1896A precore mutation is rarely observed in genotype A as it would disrupt an essential stem-loop structure in the ε signal essential for pregenomic RNA packaging. HBV genotype A also harbors a 6-nucleotide C-terminal insertion in the hepatitis B-e antigen (HBeAg) precursor, resulting in a variable-length HBeAg protein product observed in serum of positive patients. These molecular traits likely contribute to the specific clinical presentation of genotype A-infected patients, such as mild acute hepatitis B (AHB), longer persistence of HBsAg positivity in AHB, and increased chronicity after AHB in adults. However, genotype A shows a better response to interferon than other genotypes in chronic hepatitis B patients. Here, we review the virological and clinical characteristics of HBV genotype A that will be useful in elucidating the association among persistent viral infection, host genetic factors, and treatment in future studies.


Acute hepatitis Subtype HBsAg HBeAg Interferon 



Hepatitis B virus


Hepatocellular carcinoma




Hepatitis B-e antigen




Males who have sex with males


Acute hepatitis B


Cytotoxic T lymphocytes


Hepatitis B surface antigen


Nucleos(t)ide analogues


Alanine aminotransferase


Chronic hepatitis B



This study was funded by Japanese Ministry of Education, Culture, Sports, Science and Technology (Grant No. 16736857).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Japanese Society of Gastroenterology 2017

Authors and Affiliations

  • Kiyoaki Ito
    • 1
    Email author
  • Masashi Yoneda
    • 1
  • Kazumasa Sakamoto
    • 1
  • Masashi Mizokami
    • 2
  1. 1.Department of GastroenterologyAichi Medical University School of MedicineNagakuteJapan
  2. 2.The Research Center for Hepatitis and ImmunologyNational Center for Global Health and MedicineIchikawaJapan

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