FILE - A patient holds the medications she takes to slow the progression of her multiple sclerosis, Feb. 24, 2015.
FILE - A patient holds the medications she takes to slow the progression of her multiple sclerosis, Feb. 24, 2015.

Scientists have discovered that a single genetic mutation can cause multiple sclerosis.  The new evidence could lead to a cure for a disease that cripples millions of people.

It’s long been thought that multiple sclerosis was caused by some vague interplay among certain genes that made contracting MS more likely, when triggered by some environmental factor, such as a viral infection or vitamin deficiency.  

But Canadian researchers have discovered, at least in cases of a severe form of MS called primary progressive, that a single mutated gene can dramatically increase the risk for developing the neurological disorder.

An estimated two million people around the world have the disease.

Researchers at the University of British Columbia in Vancouver studied a large database assembled over the years of 2,000 Canadian families with members who had MS.  

The investigation led them to two families that carried a mutation in a single gene called NR1H3. Family members suffered from the severest form of multiple sclerosis.

Medical geneticist Carles Vilariño-Güell, a senior author of a paper published in the journal Neuron, notes that 15 to 20 percent of MS cases were thought to be hereditary but that’s never been proved.

“The other genes that were previously described increased the risk of disease by.. at most three percent. With this mutation, your risk is 60 to 70 percent. So, that’s a 600 to 700 [percent] increase in comparison to the general population. And that’s what really makes this completely different from other genetic findings ," said Vilariño-Güell.

Mice with a normal copy of NR1H3 developed neurological problems when the gene was knocked out. The problems included a decrease in the production of myelin, a protein insulation on the outside of neurons that speeds the electrical impulses that control movement. A common symptom of multiple sclerosis is muscle weakness and a loss of coordination.

Much research is devoted to trying to repair myelin in MS patients.  Currently, drugs to treat it only slow down progression of the disease. They do not cure it.

Discovery of a single genetic defect as the cause of MS, according to Vilariño-Güell, could mean it may one day be possible to repair the gene, curing the crippling neurological disorder.

“You know, the more understanding we have of the mechanism of disease for all these families allow us to develop different treatments for different forms of the disease," said Vilariño-Güell.

Researchers will also continue their search for a single genetic cause for the most common form of multiple sclerosis, relapsing remitting MS, in the hopes that it too might be cured.