Parkinson’s disease is a multisystem neurodegenerative disease with a vast heterogeneity in terms of clinical presentations and etiological factors. In a minority of cases (approximately 5% of patients) a clear genetic cause is involved. In most patients, the cause is unknown and probably implicates the cumulative result of numerous genetic and environmental insults and their interactions in the context of ageing. No curative treatment is currently available for Parkinson’s disease. Parkinson’s disease prevalence and incidence are growing worldwide and there is an urgent need to find curative if not modifying treatments.

Further studies are required to better clarify the etiology of Parkinson’s disease. Among them, epidemiological studies allow the identification of protective and harmful environmental contributors in order to provide arguments towards future interventions based upon modifiable risk factors. Basic science studies are also critical to better understand the specific mechanisms at work in Parkinson’s disease. Recently, a growing body of evidence has demonstrated the important role of gut microbiota in Parkinson’s disease.

We hereby describe a large cross-sectional population-based prevalence study as well as a retrospective incidence study that we undertook to ascertain for the first time in Switzerland the frequency of Parkinson’s disease and other types of degenerative and non-degenerative parkinsonism. This study provided an extensive overview of age-specific, sex-specific and age-adjusted prevalence and incidence of non-degenerative and degenerative forms of parkinsonism among which Parkinson’s disease is the most common cause. We then performed a subsequent study using an original approach coupling the geographic distribution of PD prevalent cases with spatial statistics. This study showed clusters of high Parkinson’s disease prevalence and supported a link between Parkinson’s disease and air pollution. The final study investigated the oral microbiota in Parkinson’s disease and we demonstrated that an oral dysbiosis (i.e. a disequilibrium in the oral commensal microbial community) is present in Parkinson’s disease.