title: Quantitative subtyping of hepatitis B virus reveals complex dynamics of YMDD motif mutants development during long-term lamivudine therapy.
abstract: OBJECTIVE
  Treatment of chronic hepatitis B (CHB) with lamivudine (3TC) is limited by development of drug-resistant mutants at the YMDD motif. We aimed to validate the use of mass spectrometry to detect YMDD mutants and quantify viral subpopulations.
  
  
  METHODS
  A total of 21 Chinese patients with severe acute exacerbation of CHB treated with 3TC were studied. Serial serum samples were tested for wild-type and YMDD mutants using matrix assisted laser desorption/ionization time-of-flight mass spectrometry. INNO-LiPA assay was performed for comparison.
  
  
  RESULTS
  At a median follow-up of 192 weeks, 11 patients developed YMDD mutants (six had YIDD, four had YVDD and one had YV/IDD). Mass spectrometry was concordant with INNO-LiPA in all but one patient, in which INNO-LiPA detected coexistence of YIDD and YVDD but mass spectrometry and direct sequencing detected YVDD only. Mass spectrometry was able to reliably detect a minor hepatitis B virus (HBV) subtype at 5% or above. By serial quantitative measurement, several patterns of viral dynamics were observed. In some cases, YMDD mutants dominated the whole viral population. In other cases, the proportion of YMDD mutants fluctuated with time. When more than one mutant was present (that is, YIDD and YVDD), the different mutants might dominate during different time periods.
  
  
  CONCLUSIONS
  Mass spectrometry is an accurate and cheap method for the detection of YMDD mutants, even in the presence of overwhelming wild-type HBV. We observed some intriguing mutant viral dynamics during 3TC treatment. Further studies are needed to clarify whether they have any clinical significance.
authors.affiliation: Stanley Ho Centre for Emerging Infectious Diseases, The Chinese University of Hong Kong, Hong Kong. cmding@cuhk.edu.hk
authors.forename: Chunming
authors.initials: C
authors.lastname: Ding
authors.forename: Vincent W S
authors.initials: VW
authors.lastname: Wong
authors.forename: Katherine C K
authors.initials: KC
authors.lastname: Chow
authors.forename: Hoi-Yun
authors.initials: HY
authors.lastname: Chan
authors.forename: Alex Y
authors.initials: AY
authors.lastname: Hui
authors.forename: Grace L H
authors.initials: GL
authors.lastname: Wong
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
authors.forename: Joseph J Y
authors.initials: JJ
authors.lastname: Sung
authors.forename: Henry L Y
authors.initials: HL
authors.lastname: Chan
mesh_terms: D000328:Adult; D000368:Aged; D020816:Amino Acid Motifs; D004334:Drug Administration Schedule; D024882:Drug Resistance, Viral; D005260:Female; D005500:Follow-Up Studies; D006515:Hepatitis B virus / Q000145:classification / Q000187:drug effects* / Q000235:genetics*; D019694:Hepatitis B, Chronic / Q000188:drug therapy* / Q000821:virology*; D006801:Humans; D019259:Lamivudine / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D017354:Point Mutation; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D019562:Viral Load
chemical_list: D019259:Lamivudine