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Thursday, October 24, 2013

Inherited herpes virus

HHV-6 being released from a lymphocyte
Three words you don’t want to hear are ‘inherited herpes virus’. It’s bad enough that herpes is so contagious, but now we learn that the virus can be integrated into the genome. In other words, according to researchers led by Yan Huang of the University of Leicester, some people are conceived with herpes. To make matters worse, herpes virus can ‘escape’ from its chromosomal home and become a free agent. 
There are actually lots of different human herpes viruses (HHVs). You know one common type (HHV-3) as chickenpox. Most of these viruses can lay low in the body, persisting without detection for many decades. However, the viral nucleic acids usually remain separate from those of the host. In the case of HHV-6, the researchers found that the viral DNA had become incorporated into the host cell's genome. Apparently, about 0.8% of the British population were HHV-6 carriers.

More specifically, the virus integrates into the telomeres at the ends of chromosomes. This region is particularly unstable and made more so by the addition of the viral DNA. This makes it more likely that the viral DNA will be shed from the ends of the chromosomes. Once this happens, it’s possible for the virus to infect new cells. 

These data suggest that a person could be born with HHV-6 already present within the DNA he inherited from a parent, and that the embedded virus could at any point cause a full blown infection. While this isn’t good news for anyone, it’s especially problematic for immuno-compromised blood and organ recipients. Currently, donation programs screen blood products for infectious agents but not for gene sequences that might become reactivated at any moment.

Yan Huang, Alberto Hidalgo-Bravo, Enjie Zhang, Victoria E. Cotton, Aaron Mendez-Bermudez, Gunjan Wig, Zahara Medina-Calzada, Rita Neumann, Alec J. Jeffreys1, Bruce Winney2, James F. Wilson3, Duncan A. Clark, Martin J. Dyer, & Nicola J. Royle (2013). Human telomeres that carry an integrated copy of human herpesvirus 6 are often short and unstable, facilitating release of the viral genome from the chromosome Nucleic Acids Research DOI: 10.1093/nar/gkt840.