Mutations in the non-structural protein 5A gene in patients with chronic hepatitis C virus 1b infection during repeated interferon treatment

It has been previously reported that the non-structural region 5A (NS5A) of the hepatitis C virus (HCV) includes an interferon sensitivity determining region (ISDR) and that amino acid substitutions in this region are closely associated with the response to interferon (IFN) treatment. We assessed the clinical significance of serial changes of amino acid sequences in the ISDR during repeated IFN treatment in patients with chronic hepatitis C (genotype 1b), related to serum HCV RNA load. During treatment, additional amino acid substitutions in the ISDR were observed in four of eight patients (50% 2/5 of complete responders (CR); 2/3 of non-responders (NR). However, comparing these amino acid substitutions to wild-type ISDR, the number of amino acid mutations was limited to only one amino acid identified in two CRs. The virus load changed regardless of the amino acid substitutions in the ISDR during treatment, and the wild-type and intermediate type (with less than three amino acid substitutions) showed wide variations in virus load. These data indicate that amino acid mutations in the ISDR, which indicate the switch to mutant-type do not occur easily even during repeated IFN treatment, and the additional amino acid substitutions in the ISDR are not a sensitive marker during repeated IFN treatment. In cases where virus load is used as a marker of response to repeated UN treatment, serial examinations are necessary to determine the precise virus load levels.