Genotypes of TT virus (TTV) compared between liver disease patients and healthy individuals using a new PCR system capable of differentiating 1a and 1b types from others

TT virus (TTV) lacks obvious pathogenicity; almost all of the infected hosts are symptom-free. A possibility remains, however, that certain strains can cause liver disease while most others are non-pathogenic. Genotypes 1a and 1b have been proposed to contain such pathogenic strains. To test this possibility, we constructed a PCR system capable of detecting TTV of the 1a and 1b genotypes differentially from the other genotypes, and compared the frequencies of these genotypes between patients with liver disease of unknown etiology (n = 42) and healthy individuals (n = 50). The assay comprised 3 steps: i) PCR to amplify a 3.2-kb fragment using universal primers; ii) 2nd-round PCR, starting from the 3.2-kb amplicon, for a similar to 280-nt fragment by use of genotype 1-specific primers; and iii) digestion of the similar to 280-nt amplicon with MboI and BanI to discriminate between la and Ib. Eventually, 40 (95%) of the patients and 47 (94%) of the controls were positive for the 3.2-kb amplicon, and the 1a, 1b, 1a+1b, and non-1 genotypes of TTV were found in 2 (5%) vs 4 (9%), 5 (13%) vs 4 (9%), 1 (3%) vs 1 (2%) and 32 (80%) vs 38 (81%) of the 40 patients and 47 controls, respectively: the distribution was almost identical between the two groups. The hypothesis that the genotype 1 of TTV may be more closely associated with liver disease than other genotypes was not supported by this study.