Sequence diversity of hepatitis C virus 6a within the extended interferon sensitivity-determining region correlates with interferon-alpha/ribavirin treatment outcomes

Studies on the association between sequence variability of the interferon sensitivity-determining region (ISDR) of hepatitis C virus and the outcome of treatment have reached conflicting results. In this study, 25 patients infected with HCV 6a who had received interferon-alpha/ribavirin combination treatment were analyzed for the sequence variations. 14 of them had the full genome sequences obtained from a previous study, whereas the other 11 samples were sequenced for the extended ISDR (eISDR). This eISDR fragment covers 192 bp (64 amino acids) upstream and 201 bp (67 amino acids) downstream from the ISDR previously defined for HCV 1b. The comparison between interferon-alpha resistance and response groups for the amino acid mutations located in the full genome (6 and 8 patients respectively) as well as the mutations located in the eISDR (10 and 15 patients respectively) showed that the mutations I2160V, I2256V, V2292I (P < 0.05) within eISDR were significantly associated with resistance to treatment. However, the extent of amino acid variations within previously defined ISDR was not associated with resistance to treatment as previously reported. Four amino acid variations I248V (P = 0.03–0.06) within E1, R445K (P = 0.02–0.05) and S747T (P = 0.03) within E2, I861V (P = 0.01) within NS2 which located outside the eISDR may also associate with treatment outcome as identified by a prescreening of variations within 14 HCV 6a full genomes.