Dear Doctor: What’s all this I’m hearing about Parkinson’s disease having something to do with the gut? I thought it was about the nervous system and the brain.

Dear Reader: You’ve zeroed in on an intriguing area of inquiry into Parkinson’s disease in which new information emerges seemingly every week. With each new link between Parkinson’s and the gastrointestinal tract, researchers edge closer to uncovering the causes of the disease, as well as identifying novel avenues of treatment.

It’s estimated that more than a million people are living with Parkinson’s disease in the United States, and about 60,000 new cases get diagnosed each year. Symptoms typically arise in people age 50 and older, and with millions of baby boomers reaching that threshold, the need for effective treatments is ever more pressing.

Parkinson’s is a progressive disease of the nervous system in which nerve cells and certain other structures deep within the brain begin to deteriorate for reasons that are not yet fully understood. This leads to a deficit of dopamine, a neurotransmitter that sends signals to nerve cells and helps us achieve smooth and deliberate movement. The symptoms of Parkinson’s — including tremors, rigidity, problems with gait and a general slowing of movement — arise from these and other changes. As a result, much of the research into Parkinson’s disease has focused on the brain and nervous system.

In recent years, however, scientists have begun to turn their attention to something known as the gut-brain axis. This is a term for the variety of ways in which the gut communicates with the brain, including via the nervous system and the endocrine system, and signaling mechanisms built into the immune system. Among the factors that influence these communications are the trillions of microorganisms that live within our intestinal tract. This has led scientists to explore how the microbiome may play a role in neurodegenerative diseases, including Parkinson’s, and how it might be harnessed in treatments — or even a cure.

One study followed a group of patients who underwent a procedure that removes portions of the vagus nerve, which runs throughout the body and links the brain and the gut. Five years after the surgery, these patients were found to have a 40% lower incidence of Parkinson’s disease than those whose vagus nerve remained intact.

In another study, conducted in mice bred to be susceptible to Parkinson’s disease, researchers saw a surge in Parkinson’s symptoms when the mice were implanted with fecal samples from Parkinson’s patients. This didn’t happen in the mice implanted with fecal samples from healthy adults.

Previous research has found that the same abnormal protein clumps that form in the brains of patients with Parkinson’s disease are also present in the gut. And from the time that Dr. James Parkinson first identified the disease in 1817, health care professionals have noted that symptoms like constipation and gastrointestinal distress often develop in the years prior to neurological symptoms. All of this has led to increasing speculation that Parkinson’s disease originates in the gut and spreads to the brain, and has set the stage for exploring gut-based therapies and a potential cure.

Eve Glazier, MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu, or write Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA 90024. Owing to the volume of mail, personal replies cannot be provided.

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