Two separate studies have raised hopes that scientists may one day be able to combat the debilitating effects of Parkinson's disease.
The degenerative disorder is caused by the destruction of brain cells that produce the chemical dopamine, and symptoms include tremors, rigid muscles, and difficulty walking.
In the first trial, experts at Weill Medical College, part of Cornell University in New York, found gene therapy injections to the brain can significantly ease the condition.
Eleven men and one woman were injected with a virus carrying the GAD (glutamic acid decarboxylase) gene, which calms over-excited brain cells.
Within three months the patients made "substantial" improvements in movement, and these continued for at least a year, the research published in The Lancet shows.
The second pioneering study in the journal Science may eventually lead to drugs with the potential to cure Parkinson's.
Doctors from Massachusetts General Hospital Institute for Neurodegenerative Disease in Boston found that blocking the action of a brain protein called SIRT2 may help prevent damage to neurons.
The findings could lead to new drugs for Parkinson's that may also aid the fight against other brain diseases associated with ageing, such as Huntington's and Alzheimer's.
Study leader Dr Aleksey Kazantsev said: "We have discovered a compelling new therapeutic approach for Parkinson's disease, which we expect will allow our scientists to pursue innovative new drugs that will treat and perhaps even cure this disorder."