Human Herpes Virus 6B Is Associated With Mesial Temporal Lobe Epilepsy

MTLE is a common, severe, type of epilepsy that usually begins in childhood. Mesial temporal sclerosis is a change often seen in the brains of patients with this form of epilepsy. Temporal lobectomy is often used to control MTLE. HHV6 is usually acquired in early childhood - more than 90% of the general population can be shown to have been infected with the virus. After primary infection, HHV-6 can persist lifelong in some white blood cells, salivary glands, and in the central nervous system. Two HHV-6 variants are known, HHV-6A and HHV-6B. Active infection or reactivation of HHV-6 in the brain has been previously shown to be associated with neurological disorders, including epilepsy and encephalitis.

As well as showing the presence of viral DNA in patients with MTLE, in additional studies in one patient who had surgery over many months because of recurrent epilepsy, the researchers were able to detect an antigen (HHV-6 gp116/54/64), which is specific for HHV-6B, in astrocytes (primary brain cells). Finally, the authors showed that infection of cell cultures of astrocyes infected with HHV-6 showed a marked decrease in the expression of one protein, EAAT, which is known to be involved in transmitting glutamate across cell membranes; glutamate is a substance that acts to carry signals within the brain.

Overall, the researchers have now have detected HHV-6B in 15 of 24 patients with mesial temporal sclerosis or MTLE, in contrast to zero of 14 with other syndromes. If these findings are confirmed in other groups of patients with this form of epilepsy, it may open up new avenues of therapy.

Citation: Fotheringham J, Donati D, Akhyani N, Fogdell-Hahn A, Vortmeyer A, et al. (2007) Association of human herpesvirus- 6B with mesial temporal lobe epilepsy. PLoS Med 4(5): e180.(http://medicine.plosjournals.org/perlserv/"request=get-document&doi=10.1371/journal.pmed.0040180)