Image credit: cooldesign
BY SARAH OWENS
Parkinson's disease may start in the gut before it spreads to the brain, according to a study published online on April 26 in Neurology. Researchers found that people who underwent a truncal vagotomy—a procedure in which part of the vagus nerve, which connects the stomach to the brain, is removed—appeared to have a lower risk of developing Parkinson's disease.
Vagus Nerve Factor
In Parkinson's disease, insufficient levels of the chemical dopamine in the brain lead to tremors, movement and balance problems, and other symptoms such as loss of smell, depression, and constipation. But while Parkinson's is considered to be a disease of the brain, researchers have wondered if its origins may extend to other parts of the body.
A theory called the Braak hypothesis suggests that alpha-synuclein, a protein thought to play a role in the disease, spreads to the brain from the stomach via the vagus nerve, which connects the brain with the heart, lungs, and digestive tract and is involved in unconscious body functions like heart rate. Studies on rats and mice have appeared to support this theory, showing that animals who had surgery to remove part of the vagus nerve had a decreased risk of developing Parkinson's disease.
To see if the connection held true for humans, too, researchers at universities in Sweden and the United States gathered data from nationwide health registers in Sweden and identified 9,430 people who underwent a vagotomy between 1970 and 2010 and matched them with 377,200 people who did not have a vagotomy. They followed the patients until they were diagnosed with Parkinson's disease, died, left Sweden, or until the end of 2010—whichever happened first.
A total of 4,930 patients developed the disease over the follow-up period. The researchers found no association between Parkinson's and selective vagotomy, in which nerves are removed from the stomach only. But people who underwent a truncal vagotomy—in which nerves are removed from multiple organs, including the stomach, liver, and gall bladder—were somewhat less likely to develop the disorder.
The risk reduction disappeared 20 years post-surgery, though, which suggests that vagotomy may simply delay, rather than prevent, the disorder. But the researchers believe that what happens in the gut may influence the development of Parkinson's disease, and, in turn, explain why gastrointestinal symptoms such as constipation sometimes show up long before movement symptoms, the study authors say.
There is still much to learn about the origins of the disease, including how alpha-synuclein is transmitted through the vagus nerve, the authors say.
In the meantime, Parkinson's disease research is thriving. In March, the FDA approved a new treatment, safinamide (Xadago), for patients with Parkinson's who take levodopa/carbidopa and experience frustrating "off-times"—periods of uncontrolled movement. Another study published in March found that just a small amount of daily exercise resulted in a big reduction in Parkinson's risk. Browse our entire collection of stories on Parkinson's at bit.ly/NN-Parkinsons.