Australian scientists Friday said they have discovered a gene abnormality responsible for the crippling condition known as Lou Gehrig's disease, which causes gradual paralysis in sufferers.
Researchers hope the breakthrough will eventually lead to a cure for the illness, also known as amyotrophic lateral sclerosis (ALS), and help pinpoint a more general cause for motor neurone disease.
Scientists at the ANZAC Research Institute based at Sydney's Concord Hospital said their research suggested the TDP-43 protein produced by the gene abnormality is toxic.
The disease is named after Lou Gehrig, a US baseball player from the 1920s and 1930s whose career was cut short by the condition.
Sufferers had been known to have abnormal deposits of TDP protein in dying nerve cells but it was thought the build-up could be caused by damaged cells trying to repair themselves.
But University of Sydney Professor Garth Nicholson said his research, conducted in collaboration with experts at Kings College London, suggested the protein itself was causing the sickness.
"What we've found is that these actual mutations cause the disease in these rare cases," he told AFP.
He said the research, published in the journal Science, was backed up by the findings that TDP abnormalities were found not just in those motor neurone disease sufferers with the rare genetic abnormality but also those without it.
"People with the sporadic (isolated cases of) motor neurone disease, the common variety, have abnormal collections of this protein in their dying neurones," he said.
"How TDP builds up in sporadic motor neurone disease cases with a normal gene is going to be the subject of more research," Nicholson said.
"Possibly it could be an environmental factor, or another gene overacting -- we don't know what's causing the protein accumulation."
Nicholson said the research could lead to better treatments for the disease, for which there is no cure and which generally proves fatal within three to five years by killing the nerves that control muscle function, eventually leaving sufferers unable to move, breathe, eat or drink.
"Maybe we can regulate this gene better, turn it down, retune it so it behaves normally. That might prevent or cure the disease," he added.