SILENT HEPATITIS-B VIRUS MUTANTS ARE RESPONSIBLE FOR NON-A, NON-B, NON-C, NON-D, NON-E HEPATITIS

Since the recent introduction of diagnostic kits for hepatitis C and E , some cases of non-A, non-B, non-C, non-D, non-E hepatitis (so-called hepatitis Fl have been revealed. We attempted to demonstrate that so- called hepatitis F is caused by hepatitis E virus (HBV) variants. Poly merase chain reaction (PCR) was used to amplify serum HBV DNAs from 20 patients with acute hepatitis and 20 patients with chronic hepatitis who had been diagnosed as having so-called hepatitis F on the basis of conventional serological markers. The PCR technique successfully ampl ified HBV DNAs in 18 (90%) cases of acute hepatitis and 17 (85%) cases of chronic hepatitis. Sequencing of HBV DNAs of six patients (acute 3 , chronic 3) revealed equally a T-to-C mutation of DR2 and an 8-nucleo tide deletion of the 3'-terminus of the X gene coding region, giving r ise to the generation of a C-terminally truncated X protein and probab le damage to the enhancer II/core promoter elements. These mutations o f the X gene coding region may lead to suppression of replication and expression of HBV DNAs. Thus virtually all cases of so-called hepatiti s F appear to be caused by ''silent'' HBV mutants, at least in Japan.