Published online Sep 7, 2019. doi: 10.3748/wjg.v25.i33.4985
Peer-review started: June 17, 2019
First decision: July 21, 2019
Revised: July 30, 2019
Accepted: August 19, 2019
Article in press: August 19, 2019
Published online: September 7, 2019
Hepatitis B virus (HBV) DNA polymerase mutations usually occur to long term use of nucleos(t)ide analogues (NAs), but they can occur spontaneously in treatment-naïve chronic hepatitis B (CHB) patients. The naturally occurring HBV-DNA polymerase mutations might complicate antiviral therapy with NAs, leading to the generation of drug-resistant viral mutants and disease progression. The most common substitutions are known to be YMDD-motif mutations, but their prevalence and the influence on antiviral therapy is unclear.
HBV DNA polymerase mutations have been known to be prevalent in treatment-naïve CHB patients infected with HBV genotype C2 strains. But there is still controversy regarding prevalence of the naturally occurring rtM204I mutations prior to antiviral treatments. Moreover, the clinical characteristics of the naturally occurring rtM204I mutations have not been fully elucidated.
The objective of this study was to determine the prevalence and clinical characteristics of naturally occurring rtM204I mutations in treatment-naïve patients infected with HBV genotype C2 strains by using a newly developed locked nucleotide probe (LNA probe) based real time PCR (LNA-RT-PCR) method, which can detect subspecies at 5% of the circulating HBV population.
The retrospective study enrolled a total of 410 treatment-naïve CHB patients infected with HBV genotype C2 strains. Among the 410 patients, 232 were treated with NAs for at least 12 mo. Significant fibrosis was defined as fibrosis-4 index > 3.25 or aspartate aminotransferase to platelet ratio index > 1.5. Complete viral response (CVR) during NAs was defined as undetectable serum HBV DNA (< 24 IU/mL). The rtM204I variants were analyzed by a newly developed LNA RT-PCR method.
The LNA-RT-PCR could discriminate rtM204I mutant-type (17 patients, 4.2%) from rtM204 wild-type (386 patients, 95.8%) in 403 of 410 patients (98.3% sensitivity). Multivariate analysis showed that naturally occurring rtM204I variants were more frequently detected in patients with significant fibrosis [odd-ratio (OR) 3.397, 95% confidence-interval (CI) 1.119-10.319, P = 0.031]. Of 232 patients receiving NAs, multivariate analysis revealed that achievement of CVR was reversely associated with naturally occurring rtM204I variants prior to NAs treatment (OR 0.014, 95%CI 0.002-0.096, P < 0.001). Almost patients receiving tenofovir achieved CVR at 12 mo of tenofovir, irrespective of pre-existence of naturally occurring rtM204I mutations (CVR rates: patients with rtM204I, 100%; patients without rtM204I, 96.6%), whereas, pre-existence of naturally-occurring rtM204I-mutations prior to NAs significantly affects CVR rates in patients receiving entecavir (at 12 mo: Patients with rtM204I, 16.7%; patients without rtM204I, 95.6%, P < 0.001).
The newly developed LNA-RT-PCR method can detect pre-existing rtM204I variants with high sensitivity in NAs-naïve CHB patients. rtM204I mutations can occur spontaneously with a rate of approximately 4% in treatment-naïve patients infected with HBV genotype C2. The rtM204I variants more frequently pre-existed in patients with significant fibrosis, and the pre-existence of rtM204I variants was associated with incomplete responses to NAs. Tenofovir is a more suitable treatment than entecavir for CHB patients carrying the naturally occurring rtM204I mutations.
The detection of pre-existing rtM204I variants with the newly developed LNA-RT-PCR method could play a relevant role in the clinical management of NA-naïve patients with CHB genotype C2 infection. Further prospective studies should be performed to verify our conclusions.