HHV-6 in Epilepsy

Researchers have long known that viruses can cause seizures in infants, and viruses have been suspected in epilepsy but direct evidence was lacking, in part because there are no good tests available to determine if a patient has a smoldering infection in the brain tissue. An intriguing paper by a Japanese researcher in 1993 suggested that HHV-6B plays a role in recurrent seizures, but the possibility of viral etiology was largely ignored until recently.

An important paper just published by Steve Jacobson and colleagues at the NINDS demonstrates that as many as two thirds of patients with Mesial Temporal Lobe Epilepsy (MTLE) may in fact suffer from a chronic HHV-6B infection.

Jacobson’s research suggests that HHV-6 causes a dysfunction in the astrocytes leading to the injury of the sensitive neurons in the hippocampus that trigger MTLE. Although this virus is ubiquitous, infecting over 95% of the population by the age of two, it can persist chronically in the brain and reactivate years after the initial infection. (Fotheringham, 2007.)

HHV-6 is a difficult virus to detect in the blood or even in the spinal fluid and serum, as it tends to stay in the tissues and not circulate. So Jacobson, who heads the Virology Immunology Section at the NINDS decided to look at the brain tissue from 16 patients who had portions of their brain tissue removed as treatment

for refractory MTLE. He found 11 of 16 patients with MTLE (but 0 of 7 control patients) had high levels of HHV-6B DNA.

Furthermore, Jacobson was able to shed some light on the mechanism by which the virus could cause epilepsy by demonstrating that HHV-6B infection induces a deficiency in the transport of glutamate. This transporter deficiency is known to be implicated in MTLE, but the reason for the deficiency has never been understood. The glutamate transport dysfunction is believed to result in injury to neurons in the hippocampus that trigger MTLE.

There is an urgent need to develop a more sensitive diagnostic technique that can detect chronic viral infection in the brain, as well as to explore the use of antiviral treatment for HHV-6B related MTLE.