In the study, more than 70 percent of patients with the relapsing-remitting form of MS showed an increased immune response to human herpes virus-6 (HHV-6) and approximately 35 percent of all MS patients studied had detectable levels of active HHV-6 in their serum. Scientists believe that there may be a point in time during the progression of MS when the virus, which lies dormant in the body for years, reactivates, accounting for its presence in a subset of MS patients. The study appears in the December 1997 issue of Nature Medicine.
"We expect that currently available antiviral treatments—for example, acyclovir—might one day be applied successfully to MS," said Steven Jacobson, Ph.D., Chief of the NINDS Viral Immunology Section and the study’s principal investigator. "We’ve suspected a possible role for a virus in MS for quite some time, and these results certainly point to this particular virus. But we need to know more before we move to the clinical trial stage."
As many as 350,000 Americans are affected by MS, which is most often diagnosed in patients between the ages of 20 and 40 and is characterized by muscle weakness, visual disturbances, and a variety of other neurological impairments. The array and severity of symptoms varies widely from patient to patient and women are more likely to be affected than men. The most common form of MS is the relapsing-remitting type. In this type of MS, new symptoms appear or existing ones become more severe, followed by periods of partial or total recovery. These flare-ups of new or intensified symptoms last for variable amounts of time. A second form of MS is a chronic and progressive one in which symptoms steadily worsen. Either form can lead to disability and paralysis.
"We’ve thought for a long time that genetics, an autoimmune factor, or something in the environment—like a virus—might cause MS," says Dr. Jacobson. "One can certainly make the case for a combination of these factors, namely that a small group of individuals may be genetically susceptible to a virus. If the HHV-6 virus is really behind MS, then we also need to know why infection with such a common virus causes disease in so few people."
HHV-6 is relatively new to scientists and is known to cause a common childhood illness, roseola. HHV-6 is known to be present in 90 percent of the adult American population as a result of infection during the first few years of life.
Scientists believe that the reactivation of HHV-6 virus may be associated with the breakdown of the protective covering of nerves, called myelin. Reactivation is characteristic of herpes viruses.
In the study, investigators screened the serum of 102 individuals, 36 of whom had MS. Of the 22 individuals with the relapsing-remitting form of MS, 73 percent had an increase in immune response to an early antigen of HHV-6, compared to only 18 percent of those participants who served as normal volunteers. In addition, the scientists detected HHV-6 DNA in the serum (a marker of active virus infection) of 15 of 50 individuals with MS. All 47 individuals without MS tested negative for the presence of active HHV-6 viral infection.
Additional testing for the presence of HHV-6 virus in larger numbers of MS patients—and in patients with other autoimmune disorders—is under way.
The NINDS, one of the National Institutes of Health located in Bethesda, Maryland, is the nation’s leading supporter of research on the brain and nervous system and a lead agency for the Congressionally designated Decade of the Brain.
1 Soldan S.S., Berti, R., Salem, N., Secchiero, P., Flamand, L., Calabresi, P., Brennan, M.B. , Maloni, H.W., McFarland, H.F. , Lin, H.C., Patnaik, M. and Jacobson, S. "Association of Human Herpes Virus 6 (HHV-6) with Multiple Sclerosis: Increased IgM Response to HHV-6 Early Antigen and Detection of Serum HHV-6 DNA." Nature Medicine, Vol. 3, No. 12; December 1997; pp. 1394-1397.