Patients with Parkinson’s disease have clear changes in their gut microbiota

A study carried out at the University of Helsinki indicates that microbes in the gut and mouth could provide new perspectives on the onset of Parkinson’s disease, particularly as they have long been suspected to play a part in the disease process.

Recently, microbial inhabitants of the human body have been connected to several health problems, including Parkinson’s disease and other neurological diseases. 

In her doctoral dissertation, Velma Aho investigated the potential associations of Parkinson’s disease and human microbiota in the mouth, nose and gut, and examined the tools used to compare their abundance. Aho’s findings supported an observation according to which patients with Parkinson’s disease have less bacteria of the Prevotellaceae family in their gut than control subjects. 

“As other research groups have also demonstrated this difference in their publications, it’s emerging as one of the central changes in microbiota associated with Parkinson’s disease,” Aho states. 

Bacteria of the Prevotellaceae family have been found to be more abundant in individuals who observe a plant-based diet, but all in all their significance to the gut and health remains unclear.

Aho’s findings indicate that the bacterial communities of the gut and mouth in patients with Parkinson’s disease differ from those found in control subjects; a statistically significant difference was found in the composition of the bacterial communities, as well as in the numbers of several bacteria. The differences between bacterial communities in the gut were also identifiable in follow-up samples collected from the same study subjects two years after the initial sampling. 

Aho also identified differences in gut microbiota when the patients were divided into those with and those without symptoms suggesting irritable bowel syndrome. In this comparison too, the abundance of Prevotellaceae bacteria was highlighted as a differentiating factor. On the other hand, Aho’s study saw no difference between patients and control subjects in terms of bacteria in the nose.

Researcher ended up in the same result by using multiple tools

Research focused on human microbiota typically revolves around identifying the microbes whose numbers differ between the groups being compared, such as patients and control subjects. Aho examined samples collected from a total of 76 patients with Parkinson's disease and 76 control subjects without parkinsonian symptoms. 

She used six different tools to compare the variance of gut bacteria between the two groups. Despite the differences, all of the tools tested by Aho substantiated the observation according to which bacteria of the Prevotellaceae family are less abundant in the gut of patients suffering from Parkinson’s disease compared to control subjects. 

“As for comparing bacteria numbers, the analyses of gut microbiota carried out with six tools highlighted differences in the lists of significantly differentiated bacteria they provided. More extensive methodological comparisons are needed to make it easier for researchers to choose which tool to use,” Aho points out. 

Doctoral dissertation: 

Velma T. E. Aho, MSc, will defend her doctoral dissertation entitled "Differential abundance analyses of human microbiota in Parkinson’s disease” in the Faculty of Biological and Environmental Sciences, University of Helsinki, on 29 March 2019 at 12.00. The public defence will take place at Info Centre Korona, auditorium 2 (room 235), Viikinkaari 11. Associate Professor Paul Wilmes from the University of Luxembourg will serve as the opponent and Professor Ville Mustonen as the custos.

The dissertation will be published in the series Dissertationes Scholae Doctoralis Ad Sanitatem Investigandam Universitatis Helsinkiensis.  The dissertation is also available in electronic form through the E-thesis service.

Parkinson’s disease is the second most common neurodegenerative disease in the world. In spite of decades-long research, the cause of the non-familial form of the disease remains a mystery. For now, there is no medication available to slow down the progression of the disease, nor are there any good methods for early diagnosis, even though the earliest non-motor symptoms, such as constipation and the impairment of the sense of smell, may begin years or even decades before the onset of motor disturbances characteristic of the disease.