Scientists believe they may have found a way to treat muscular dystrophy.
Scientists say it may lead to new drugs to fight the disease
There is currently no cure for the muscle-wasting disease, the most common form of which affects one in every 3,500 children. Most die young.
But scientists at the University of California, San Francisco, say they have identified a defect in a key protein which may trigger the disease.
Writing in the journal Nature, they said the discovery could lead to new treatments to fight the disease.
Muscles contract when nerve cells release a chemical called acetylcholine.
Up until now, scientists have believed that this chemical is broken down and disappears from the body naturally.
However, scientists at the Ernest Gallo Clinic and Research Center at UCSF have now discovered that this is not the case.
They have found that the chemical is actually switched off by a transporter - a group of proteins that can travel through cells.
A similar process regulates other chemicals in the brain, such as serotonin and dopamine.
But they have also discovered that too much acetylcholine can damage muscles and cause them to degenerate - the hallmark of muscular dystrophy.
While further research is needed, the scientists believe that drugs could be used to switch this chemical off. Prozac, for instance, affects the transporter or proteins that regulate serotonin.
"We hope that these findings will ultimately lead to an effective treatment for common forms of muscular dystrophy," said Dr Steven McIntire, who led the study.
The finding also opens up the possibility for new treatments for other diseases, such as Alzheimer's.
Acetylcholine plays an important role in enabling neurons in the brain to communicate with each other.
Alzheimer's disease occurs when neurons stop communicating and eventually die, affecting memory and mental capacity.