Parkinson's Disease And The Microbiome

The human body plays host to trillions of microbes – such as bacteria, archaea, and fungi – collectively called the microbiome. Over the past few decades, it has become abundantly clear to the scientific community that the microbiome plays an essential role in our development, physical health, and mental well-being.

This latter connection, between our minds and our microbiomes, particularly in our digestive tracts, is part of our “gut-brain axis.” Many neurological diseases like Parkinson’s disease that affect our brain and behavior – often begin with digestive tract issues as the first sign

23andMe Parkinson’s Research

23andMe has focused research efforts on Parkinson’s disease since 2009. Just under half of people diagnosed with Parkinson’s disease suffer from intestinal problems, such as constipation, and other more classical symptoms associated with the disease, such as tremors and slow movement.

While researchers have identified genes and environmental factors that may contribute to the risk, for those with Parkinson’s, the cause of their disease remains unknown. For several years, it had been thought that Parkinson’s might start in the gut. The hallmark of the disease is the buildup of misfiled protein (alpha-synuclein) deposits in nerve cells in the brain. One intriguing hypothesis is that this misfiling might start in the gastrointestinal tissue, and travel through the nervous system up to the brain. This, of course, opens the possibility that the gut microbiome might play a key role in the pathological onset of Parkinson’s disease.

Most studies in the microbiome in people with Parkinson’s disease have been in small populations and so far have led to more questions than answers. In order to investigate what role the microbiome might play in the development of Parkinson’s disease, 23andMe embarked on a large microbiome study in collaboration with The Michael J. Fox Foundation for Parkinson’s Research (MJFF). 

Back in 2021, we invited over 650 23andMe customers, about two thirds of whom had reported being diagnosed with PD, to participate in the study by providing stool and saliva microbiome samples. To our knowledge, this is the largest single study to test the relationships between both the oral and gut microbiomes and Parkinson’s disease, providing us with the statistical power to uncover potentially important associations.

Participants’ samples were sequenced using a high-tech method called shotgun metageonomics, which allows us to identify not only which microbes are present in the microbiome, but genes that these microbes harbor. This gives us information of “who” is in the microbiome, and “what” they’re capable of doing. Additionally, the participants completed a deep dive survey of microbiome-related questions, such as their age, dietary habits, and biological sex. Customers with Parkinson’s also provided detailed information about their symptoms, treatment, disease milestone, and daily functioning.

The primary goal is to identify signatures of Parkinson’s disease in the microbiome. That is, are their specific microbes of specific microbial genes that are more likely to be present in people with Parkinson’s disease regardless of their age, biological sex, diet, or symptoms? Furthermore, we can identify microbes or microbial genes that are associated with specific Parkinson’s symptoms, how fast their disease has progressed, and how severe their symptoms are.

This is the first time a single study of this size sampled both the gut and oral microbiomes. In doing so, we can identify links between the microbes in our mouth and gut and how this might contribute to Parkinson’s disease. As sampling saliva is much less cumbersome than sampling stool, spit-based microbiome sampling could provide us with a much easier way to test for the presence of microbial Parkinson’s disease indicators in the future.

The study included 427 customers with Parkinson’s disease and 226 customers without PD between the ages of 50 and 69. The customers with Parkinson’s disease were diagnosed, on average, at the age of 59 years old. They reported typical motor symptoms of PD including shaking tremor (67%), slowness of movement (47%), stiffness (40%). Around one-third also reported suffering from constipation. Our microbiome can differ substantially according to where we live. The samples collected in the study were collected across all 50 states in the US, which will make the findings widely geographically applicable.

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