A major new discovery has been made towards finding the cause of multiple sclerosis (MS) - potentially paving the way for pioneering treatments.
The central nervous system disease affects roughly 2.5 million people worldwide, with many sufferers typically diagnosed in their 20s and 30s.
Although the cause has so far been a mystery, scientists believe they have found a new cellular mechanism which may trigger it.
MS causes the body's own immune system to attack myelin - the fatty "sheaths" which protect nerves in the brain and spinal cord.
This in turn leads to brain damage, a reduction in blood supply and oxygen and the formation of lesions in the body.
Symptoms of MS can be wide-ranging, including muscle spasms, mobility problems, pain, fatigue, and problems with speech.
Scientists have long suspected that mitochondria, the energy-creating "powerhouse" of the cell, plays a link in causing multiple sclerosis.
Using human brain tissue samples, researchers at the Universities of Exeter and Alberta found a protein called Rab32 is present in large quantities in the brains of people with MS - but is virtually absent in healthy brain cells.
Where Rab32 is present, the team discovered that a part of the cell which stores calcium gets too close to the mitochondria.
The resulting miscommunication with the calcium supply triggers the mitochondria to misbehave, ultimately causing toxicity for brain cells in people with MS.
Researchers do not yet know what causes an unwelcome influx of Rab32 but they believe the defect could originate at the base of the cell.
The finding will enable scientists to search for effective treatments that target Rab32 and embark on determining whether there are other proteins which could pay a role in triggering MS.
Professor Paul Eggleton, of the University of Exeter Medical School, said: "Multiple sclerosis can have a devastating impact on people's lives, affecting mobility, speech, mental ability and more.
"So far, all medicine can offer is treatment and therapy for the symptoms - as we do not yet know the precise causes, research has been limited.
"Our exciting new findings have uncovered a new avenue for researchers to explore. It is a critical step, and in time, we hope it might lead to effective new treatments for MS."
The research has been published as part of MS Awareness Week.