The researchers found that a rare genetic mutation causes a form of MS, removing doubts that certain forms are inherited.
Researchers from the University of British Columbia and Vancouver Coastal Health in Canada publish their results in the journal Neuron.
The team, led by Prof. Carles Vilarno-Guell, says they have proven that multiple sclerosis (MS) can result from a single genetic mutation on a gene called NR1H3, which produces a protein that acts as an "on-off switch" for other genes.
They explain that some of the other genes either work to stop myelin-damaging inflammation or create new myelin to repair the damage.
Myelin is the fatty material that surrounds neurons and helps send electrical signals. When myelin is damaged, it disrupts the communication between the brain and the rest of the body, producing vision problems, muscle weakness, balance issues, and cognitive impairments - hallmarks of MS.
The researchers say their findings could help uncover therapies that either target the NR1H3 gene or that neutralize the mutation's effects.
Two thirds of people with genetic mutation developed MS
To arrive at their findings, the researchers used blood samples taken from 4,400 people with MS and 8,600 blood relatives as part of a 20-year project funded by the MS Society of Canada and the Multiple Sclerosis Scientific Research Foundation.
They found the mutation in two Canadian families in which several members had a rapidly progressive type of the disease. In these families, two thirds of the people with the genetic mutation developed MS.
The investigators further explain the findings in the video below:
The researchers say that only 1 in 1,000 people with MS have this specific mutation. However, the finding uncovers the biological pathway that leads to the rapidly progressive form of MS, which accounts for 15 percent of people with the disease.
"This mutation puts these people at the edge of a cliff," says Prof. Vilarino-Guell, "but something has to give them the push to set the disease process in motion."
He and his team say their discovery could improve understanding of the more common form of MS called "relapsing-remitting," because it typically becomes more progressive.
"If you have this gene, chances are you will develop MS and rapidly deteriorate. This could give us a critical early window of opportunity to throw everything at the disease, to try to stop it or slow it. Until now, we didn't have much basis for doing that."
Dr. Anthony Traboulsee, MS Society of Canada Research Chair
Following on from this study, the researchers say that screening for this particular mutation in individuals at risk for MS could facilitate earlier diagnosis and treatment before the onset of symptoms.