Number and position of mutations in the interferon (IFN) sensitivity-determining region of the gene for nonstructural protein 5A correlate with IFN efficacy in hepatitis C virus genotype 1b infection.

To explore the relationship between responses to interferon (IFN) and the mutation patterns in the IFN sensitivity-determining region (ISDR; amino acid positions 2209-2248) in the NS5A gene of hepatitis C virus genotype 1b, a cohort of 334 patients was analyzed. The number of mutations in the ISDR was higher in patients with sustained response (SR) than in patients with transient or no response (P<.001). Patients with viruses mutated at positions 2209 (P=.02), 2216 (P=.01), or 2227 (P=.02) more frequently experienced SR than did those without these mutations. Mutation occurred most frequently at position 2218, where the presence of cysteine was significantly associated with SR. Thus, the mutation pattern in the ISDR affects the virologic response to IFN and reflects different influences on the function of the NS5A protein. ISDR sequence analysis would allow the prediction of clinical IFN efficacy in individual patients.