title: A rare HBV subgenotype D4 with unique genomic signatures identified in north-eastern India--an emerging clinical challenge?
abstract: OBJECTIVE
  HBV has been classified into ten genotypes (A-J) and multiple subgenotypes, some of which strongly influence disease outcome and their distribution also correlate with human migration. HBV infection is highly prevalent in India and its diverse population provides an excellent opportunity to study the distinctiveness of HBV, its evolution and disease biology in variegated ethnic groups. The North-East India, having international frontiers on three sides, is one of the most ethnically and linguistically diverse region of the country. Given the paucity of information on molecular epidemiology of HBV in this region, the study aimed to carry out an in-depth genetic characterization of HBV prevailing in North-East state of Tripura.
  
  
  METHODS
  From sera of chronically HBV infected patients biochemical/serological tests, HBV DNA quantification, PCR-amplification, sequencing of PreS/S or full-length HBV genomes were done. HBV genotype/subgenotype determination and sequence variability were assessed by MEGA5-software. The evolutionary divergence times of different HBV subgenotypes were estimated by DNAMLK/PHYLIP program while jpHMM method was used to detect any recombination event in HBV genomes.
  
  
  RESULTS
  HBV genotypes D (89.5%), C (6.6%) and A (3.9%) were detected among chronic carriers. While all HBV/A and HBV/C isolates belonged to subgenotype-A1 and C1 respectively, five subgenotypes of HBV/D (D1-D5) were identified including the first detection of rare D4. These non-recombinant Indian D4 (IndD4) formed a distinct phylogenetic clade, had 2.7% nucleotide divergence and recent evolutionary radiation than other global D4. Ten unique amino acids and 9 novel nucleotide substitutions were identified as IndD4 signatures. All IndD4 carried T120 and R129 in ORF-S that may cause immune/vaccine/diagnostic escape and N128 in ORF-P, implicated as compensatory Lamivudine resistance mutation.
  
  
  CONCLUSIONS
  IndD4 has potential to undermine vaccination programs or anti-viral therapy and its introduction to North-East India is believed to be linked with the settlement of ancient Tibeto-Burman migrants from East-Asia.
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Banerjee
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Rajiv Kumar
authors.initials: RK
authors.lastname: Mondal
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Madhuparna
authors.initials: M
authors.lastname: Nandi
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Sumantra
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Mousumi
authors.initials: M
authors.lastname: Khatun
authors.affiliation: Agartala Government Medical College, Tripura, India.
authors.forename: Nabendu
authors.initials: N
authors.lastname: Chakraborty
authors.affiliation: Agartala Government Medical College, Tripura, India.
authors.forename: Swatilekha
authors.initials: S
authors.lastname: Bhattacharya
authors.affiliation: Columbia University, New York, New York, United States of America.
authors.forename: Arindam
authors.initials: A
authors.lastname: RoyChoudhury
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Soma
authors.initials: S
authors.lastname: Banerjee
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Amal
authors.initials: A
authors.lastname: Santra
authors.affiliation: Tripura University, Tripura, India.
authors.forename: Samir
authors.initials: S
authors.lastname: Sil
authors.affiliation: Department of Hepatology, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Chowdhury
authors.affiliation: Agartala Government Medical College, Tripura, India.
authors.forename: Pradip
authors.initials: P
authors.lastname: Bhaumik
authors.affiliation: Centre for Liver Research, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education and Research, Kolkata, India.
authors.forename: Simanti
authors.initials: S
authors.lastname: Datta
mesh_terms: D000328:Adult; D005260:Female; D016679:Genome, Viral / Q000235:genetics*; D023281:Genomics; D005838:Genotype; D006515:Hepatitis B virus / Q000145:classification / Q000235:genetics* / Q000502:physiology; D019694:Hepatitis B, Chronic / Q000453:epidemiology / Q000821:virology; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010802:Phylogeny; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics