The neuropathological hallmark of Parkinson’s disease (PD) is the accumulation of alpha–synuclein (AS) aggregates. The identification of AS aggregates in gut biopsy specimens from people with PD may provide an opportunity to identify PD at a very early stage, prior to symptom onset. Changes in gut microbiota and inflammatory conditions (such as periodontitis) may be linked with PD onset/evolution. This project aims to explore the concept of microbiota–gut–brain axis in PD, studying gut biopsy specimens for AS aggregates, oral and intestinal microbiota, associated digestive disorders and oral health, of both patients with PD and controls.