Some healthy individuals carry human herpesvirus-6 (HHV-6) within a host chromosome, which is called inherited chromosomally integrated human herpesvirus-6 (iciHHV-6). Because iciHHV-6 is generally considered a non-pathogenic condition, it is important to distinguish iciHHV-6 from HHV-6 reactivation in immunocompromised hosts because both conditions manifest high copy numbers of the HHV-6 in peripheral blood mononuclear cells. Although fluorescent in situ hybridization (FISH) is a reliable method for the diagnosis of iciHHV-6, HHV-6-specific FISH probes are not commercially available. In our present study, we established a simple PCR-based method for producing FISH probes that can detect the chromosomal integration site of iciHHV-6 at high sensitivity. Using these probes, we confirmed that HHV-6 signals were consistently located at the telomeric region in all of the 13 iciHHV-6 individuals examined. Interestingly, in all seven Japanese iciHHV-6A patients, signals were detected exclusively on chromosome 22q. This method provides a simple and fast approach for iciHHV-6 diagnosis in the clinical laboratory.
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