A variant of a common herpes virus may play a role in the development of multiple sclerosis (MS), Swedish researchers say.

They analysed the blood of about 8 700 MS patients and a control group of more than 7 200 people without MS. They were looking for antibodies against proteins of two variants (A and B) of human herpes virus 6 (HHV-6), which has been linked with MS.

Cause unclear

MS patients were 55% more likely to have antibodies against the HHV-6A protein than the control group.

The researchers also looked a sub-group of almost 500 people who did not have MS. The risk of developing MS more than doubled for those who’d had a HHV-6A infection. The younger they were when the virus was found in their blood, the greater their future MS risk.

The findings suggest that HHV-6A may play a role in the development of MS, according to the authors of the study published in the journal Frontiers in Immunology.

MS is an autoimmune disease that affects the central nervous system, causing weakness, movement problems and tremors. Its cause is unclear, but one theory is that a virus tricks the immune system to attack the body’s own tissue.

Though previous research linked HHV-6 with MS, it couldn’t distinguish between the 6A and 6B variants. Researchers in this new study were able to do that.

Antibodies for the rest of their lives

“This is a big breakthrough for both the MS and herpes virus research,” said study co-senior author Anna Fogdell-Hahn, an associate professor of clinical neuroscience at Karolinska Institute in Stockholm.

“For one, it supports the theory that HHV-6A could be a contributing factor to the development of MS,” Fogdell-Hahn said in an institute news release. “On top of that, we are now able, with this new method, to find out how common these two different types of HHV-6 are, something we haven’t been able to do previously.”

It’s believed that as many as 80% of children are infected with the HHV-6 virus before they’re 2 years old, and many have antibodies against it for the rest of their lives.

“Both HHV-6A and 6B can infect our brain cells, but they do it in slightly different ways. Therefore, it is now interesting to go forward and attempt to map out exactly how the viruses could affect the onset of MS,” Fogdell-Hahn said.

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