Parkinson's disease, associated with a degeneration in the movement center of the brain, may have its origins in another area of the human anatomy entirely, researchers say: the gut.
More than a decade ago, a German neuropathologist named Heiko Braak suggested the disease might begin in the gut then spread to the brain.
The idea generated intense debate, but now researchers from Lund University in Sweden say they have seen some initial direct evidence that the disease is capable of migrating from the gut into the brain.
Parkinson's patients frequently complain of gastrointestinal problems that are poorly understood and the issues have been sparsely investigated with little success in finding an effective cure.
This suggests the so-called Braak's hypothesis, which holds that the process leading to Parkinson's begins in the digestive tract and in the brain's smell center, may be accurate.
In Parkinson's patients, symptoms linked with smell and digestion often occur early in the progression of the disease.
Misfolded proteins that come together in clumps and "infect" neighboring cells are thought to drive the progression; the Swedish researchers, using rats in experiments, report they have been able to track this clumping action from the gut to the brain.
Recent research has shown the gastrointestinal tract in Parksinon's patients often shows pathological alterations within peripheral neuronal networks
The culprit protein, alpha-synuclein, eventually reaches the brain's movement center with the resulting characteristic movement disorders of Parkinson's disease.
"We have now been able to prove that the disease process actually can travel from the peripheral nervous system to the central nervous system, in this case from the wall of the gut to the brain," lead researcher Jia-Yi Li says.
The exact mechanism that drives the transport of the damaging protein will be the subject of further study, the researches say.
The current findings strongly suggest the protein is transferred during communication between nerve cells, they say, a point of interaction that may be the best chance for interventions intended to stop further spread of the disease.
"In the longer term, this may give us new therapeutic targets to try to slow or stop the disease at an earlier stage," Li says.
Parkinson's is more prevalent in older individuals, with most cases beginning to display symptoms after age 50.
Around seven million people globally and one million people in the United States suffer from Parkinson's, the second most common neurodegenerative disorder after Alzheimer's disease.
