title: Evolution of wild type and mutants of the YMDD motif of hepatitis B virus polymerase during lamivudine therapy.
abstract: OBJECTIVE
  Long-term lamivudine treatment for chronic hepatitis B virus (HBV) infection induces the emergence of lamivudine resistant HBV YMDD mutant strains. The aim of the present study was to observe the clone evolution of YMDD wild type and mutant strains in pretreatment and post-treatment samples during lamivudine therapy and analyze their clinical significance.
  
  
  METHODS
  Ten serum samples (five before and five after 48 weeks of therapy) obtained from five patients chronically infected with HBV and treated with lamivudine were studied. Part of the HBV polymerase gene flanking the YMDD motif was sequenced after polymerase chain reaction (PCR) amplification. Meanwhile, 20-24 clones were selected at random from each sample and YMDD wild type and mutant strains were detected by real-time fluorimetry PCR established in our laboratory.
  
  
  RESULTS
  The YMDD mutants were not detectable in all five patients before treatment and were found in four patients after 48 weeks of therapy by sequencing directly on PCR products. Analysis of individual clones showed that the ratios of mutant strains in each of the five patients were 0, 9.5, 0, 4.5 and 5.6%, respectively, before therapy and 100, 100, 65, 100 and 0%, respectively, after 48 weeks of therapy. M552I was detected before therapy in one patient but M552V became the domain strain after therapy. Until 52 weeks of therapy, serum HBV DNA and alanine aminotransferase (ALT) breakthrough were found in two of the four patients with YMDD mutations. The fifth patient experienced breakthrough of ALT but HBV DNA remained undetectable.
  
  
  CONCLUSIONS
  The mutant strains of YMDD motif of HBV polymerase could be found in patients before lamivudine treatment, indicating that antiviral therapy allows the rapid selection of resistant strains. The replication ability of the M552V mutant strain might be stronger than that of the M552I mutant strain.
authors.affiliation: Department of Infectious Diseases, Rui Jin Hospital, Shanghai Second Medical University, Shanghai, China. zxinx2001@sohu.com
authors.forename: Xinxin
authors.initials: X
authors.lastname: Zhang
authors.forename: Chuanmiao
authors.initials: C
authors.lastname: Liu
authors.forename: Qiming
authors.initials: Q
authors.lastname: Gong
authors.forename: Shenying
authors.initials: S
authors.lastname: Zhang
authors.forename: Donghua
authors.initials: D
authors.lastname: Zhang
authors.forename: Zhimeng
authors.initials: Z
authors.lastname: Lu
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000410:Alanine Transaminase / Q000097:blood; D020816:Amino Acid Motifs / Q000235:genetics; D003001:Cloning, Molecular; D004279:DNA, Viral / Q000235:genetics*; D024882:Drug Resistance, Viral / Q000235:genetics; D015684:Gene Products, pol / Q000235:genetics*; D006509:Hepatitis B / Q000097:blood / Q000188:drug therapy* / Q000821:virology; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D019259:Lamivudine / Q000627:therapeutic use*; D009154:Mutation / Q000235:genetics*; D018894:Reverse Transcriptase Inhibitors / Q000627:therapeutic use*; D013997:Time Factors
chemical_list: D004279:DNA, Viral; D015684:Gene Products, pol; C066027:P protein, Hepatitis B virus; D018894:Reverse Transcriptase Inhibitors; D019259:Lamivudine; D000410:Alanine Transaminase