The debilitating effects of Parkinson's disease (PD) cause suffering for an increasing number of people. However, scientists still don't know why some people develop the condition. Now researchers in Denmark have taken an important step toward gaining a better understanding of the disease. A major study from Aarhus University and Aarhus University Hospital suggests that the neurological condition may actually begin in the gut.
Parkinson's disease is a chronic, neurodegenerative disease that affects motor function and movement. Around 1 in every 1000 people develop the progressive disease, which means that, according to the Parkinson's Disease Foundation, nearly one million people in the U.S. are living with the condition. The first signs of the disease are most often seen between the ages of 50 and 60.
The disease occurs when certain neurons — the brain's nerve cells — stop working. These neurons produce dopamine, a chemical the body uses to send out messages concerning movement and coordination. As the condition worsens, the amount of dopamine produced by the brain is reduced and the sufferer becomes unable to control bodily movement. Patients may experience tremors in the hands, legs and face; changes in speech; slowness of movement; difficulty with balance and stiffness of the limbs. Sufferers can also experience a host of other symptoms including fatigue, sleep disorder and generalized pain.
Although the underlying cause of PD is unknown and there is presently no cure, limited treatment options do exist. Medications that improve the supply or effects of dopamine or medical procedures like deep brain stimulation can manage symptoms of the disease. It is hoped the new research will lead to greater understanding and more effective treatment for those with PD.
The new research from Aarhus University in Denmark suggests that Parkinson's disease may actually begin in the gastrointestinal tract and spread through the vagus nerve to the brain. This nerve represents the long line of communication that stretches from the brain to the abdomen via several organs including the heart, lungs and digestive tract. The nerve is part of the body's involuntary nervous system that controls unconscious body processes like heart rate and food digestion.
One of the functions of the vagus nerve is to control the amount of acid the stomach produces. People suffering from ulcers may be generating too much acid and so doctors may consider a vagotomy — the cutting of the nerve to reduce acid production. In the Danish study, researchers looked at 14,883 patients who had undergone a vagotomy.
Elisabeth Svensson from Aarhus University explains the theory behind the study of these patients: "Between approximately 1970 and 1995 this procedure was a very common method of ulcer treatment. If it really is correct that Parkinson's starts in the gut and spreads through the vagus nerve, then these vagotomy patients should naturally be protected against developing Parkinson's disease."
The idea turned out to be correct, says Svensson: "Our study shows that patients who have had the entire vagus nerve severed were protected against Parkinson's disease. Their risk was halved after 20 years. However, patients who had only had a small part of the vagus nerve severed were not protected. This also fits the hypothesis that the disease process is strongly dependent on a fully or partially intact vagus nerve to be able to reach and affect the brain."
Previous ideas about the relationship between PD and the vagus nerve have led to investigations using animals and to laboratory cell studies. However, the current project is the largest study so far and the first in humans. The research project was supported by the Danish Parkinson's Disease Association and Program for Clinical Research Infrastructure.
The research — the results of which have just been published in the international journal Annals of Neurology — appears to show a strong link between gastrointestinal problems and Parkinson's disease. It is known that many patients who develop PD have previously suffered from gastrointestinal problems. "Patients with Parkinson's disease are often constipated many years before they receive the diagnosis, which may be an early marker of the link between neurologic and gastroenterologic pathology related to the vagus nerve," says Svensson.
Although only an observational study, Svensson sees the research as a major step toward fighting the onset and development of PD. "Now that we have found an association between the vagus nerve and the development of Parkinson's disease," she says, "it is important to carry out research into the factors that may trigger this neurological degeneration, so that we can prevent the development of the disease. To be able to do this will naturally be a major breakthrough."