The human digestive tract contains up to a thousand different types of bacteria, which help you digest food, make vitamins and maintain your immune system. The amount of bacteria is influenced by diet, age and other variables, and is thus unique to each individual.
Filip Scheperjans, MD, PhD, and colleagues from the University of Helsinki, Finland examined the intestinal contents of 72 people with Parkinson’s and 72 without PD. Their research, funded by MJFF and published recently in Movement Disorders, revealed that people with Parkinson’s had lower levels of a certain bacterium and that concentrations of another bacterium varied among subgroups of those with PD with differing motor symptoms.
Intestines as a Window to the Brain
There is a clear effect of Parkinson’s disease on the gastrointestinal system. Nearly 80 percent of people with PD have constipation, and this condition often predates the motor symptoms of Parkinson’s by several years.
Additionally, alpha-synuclein — a protein that clumps in the brains of all people with Parkinson’s — has been found in several locations outside the brain, including the nerves controlling the intestines. Investigators question whether the abnormal protein could show up here first, causing non-motor symptoms, and later spread to the brain to cause motor symptoms.
Lastly, researchers believe the normal bacteria of the gut might affect the functioning of the gut nerves which could in turn affect the nerves of the brain.
Specific Bacterial Levels Are Affected in Parkinson’s Disease
In Dr. Scheperjans’ study, the bacteria Prevotella was present at lower levels in the guts of people with Parkinson’s disease. This bacterium aids in the creation of the vitamins thiamine and folate and the maintenance of an intestinal barrier protecting against environmental toxins. This finding may therefore have implications not only for diagnosis but also for dietary adjustments or vitamin supplementation for management of PD in the future.
In people with Parkinson’s with more severe postural instability and gait difficulty, as opposed to tremor, the bacterium Enterobacteria was present at higher levels. The reasons for this association were not clear.
Studying Intestinal Bacteria Will Advance Understanding of Parkinson’s
Deciphering information from the gut could lead to earlier and more definitive diagnosis, a better understanding of how Parkinson’s progresses, and ways to separate the populations of people with differing symptoms of PD.
If researchers determine that there are specific and consistent differences in the gut, bacteria may serve as biomarkers — objective measurements to diagnose or track PD. As the gut is much more accessible than the brain and can be analyzed through stool samples, a bacterial biomarker is an attractive prospect.
Additionally, we don’t know why people with Parkinson’s disease show such varied motor symptoms (gait problems versus tremor, for example) or who will get which. Bacterial differences may allow us to separate the subtypes of Parkinson’s and, as a result, give individuals a better idea of the symptoms and disease progression they might expect.
More Research Is Needed
Further studies are called for to learn more about the relationship between these and other gut bacteria and Parkinson’s. In the meantime, researchers are intensely studying alpha-synuclein to determine how and why this protein contributes to Parkinson’s, and its connection between the gut and the brain.
Until a disease-modifying therapy is found, symptomatic treatments, including a drug for constipation, remain under development.
In the course of Parkinson’s disease (PD), the enteric nervous system (ENS) and parasympathetic nerves are amongst the structures earliest and most frequently affected by alpha-synuclein pathology. Accordingly, gastrointestinal dysfunction, in particular constipation, is an important non-motor symptom in PD and often precedes the onset of motor symptoms by years. Recent research has shown that intestinal microbiota interact with the autonomic and central nervous system via diverse pathways including the ENS and vagal nerve. The gut microbiome in PD has not been previously investigated. We compared the fecal microbiomes of 72 PD patients and 72 control subjects by pyrosequencing the V1–V3 regions of the bacterial 16S ribosomal RNA gene. Associations between clinical parameters and microbiota were analyzed using generalized linear models, taking into account potential confounders. On average, the abundance of Prevotellaceae in feces of PD patients was reduced by 77.6% as compared with controls. Relative abundance of Prevotellaceae of 6.5% or less had 86.1% sensitivity and 38.9% specificity for PD. A logistic regression classifier based on the abundance of four bacterial families and the severity of constipation identified PD patients with 66.7% sensitivity and 90.3% specificity. The relative abundance of Enterobacteriaceae was positively associated with the severity of postural instability and gait difficulty. These findings suggest that the intestinal microbiome is altered in PD and is related to motor phenotype. Further studies are warranted to elucidate the temporal and causal relationships between gut microbiota and PD and the suitability of the microbiome as a biomarker. © 2014 International Parkinson and Movement Disorder Society