HEPATITIS-C VIRUS GENOTYPING BY MEANS OF 5'-UR CORE LINE PROBE ASSAYSAND MOLECULAR ANALYSIS OF UNTYPABLE SAMPLES

To test the theoretical possibility of 5'-UR mistyping between hepatit is C virus subtypes 1a and 1b, we combined a 5'-UR/Core line probe ass ay (LiPA) with a nested PCR system and retested 183 sera, previously g enotyped as type 1a or 1b and originating mainly from Western Europe. Eight percent of these were found to be wrongly subtyped. Based on thi s method, 3 additional subtypes of type 1 were discovered (1d-1f). Ran domly selected European type 2 sera (n = 18) were tested with a simila r type 2 5'-UR/Core LiPA. They were unexpectedly found to belong to su btype 2c in the majority of cases. Among serum samples originating fro m South-East Asia, several additional genotypes (7a, 7c, 7d, and 9a) w ere detected which had 5'-UR sequence motifs indistinguishable from ge notype 1. Based on 13,203 pairwise comparisons in the 340-bp NS5B regi on, classification into types, subtypes, and isolates was obtained in 99.8% of all cases by using the phylogenetic border value of 0.328 for subtypes/types and 0.127 for isolates/subtypes; and evidence for a 10 th major type of HCV was provided. Combination of all available HCV se quence data from the 447-bp Core/E1 region and the NS5B 340-bp and 222 -bp regions provided evidence for the existence of 10 types, including 50 subtypes. Previously, extensive studies involving genotypes 1a, 1b , 2a, and 2b indicated the importance of HCV subtyping in interferon t reatment and progression of chronic liver disease. The herein describe d expansion in the number of HCV types and subtypes should help improv e diagnosis, treatment and possibly prophylaxis of hepatitis C liver d isease.