In Parkinson’s disease (PD), motor symptoms are mainly related to the loss of dopaminergic neurons in the substantia nigra. However, neuropathological changes are much more widespread, involving the autonomic nervous system, olfactory structures, lower brainstem, and cerebral cortex. Extranigral pathology is related to a broad spectrum of non-motor symptoms (NMS) that have been increasingly recognized as an important feature of PD. Gastrointestinal dysfunction, in particular constipation, affects up to 80% of PD patients and may precede the onset of motor symptoms by years. Idiopathic constipation is one of the strongest risk factors for PD. Prolonged intestinal transit time and constipation are associated with neurodegenerative changes in the enteric nervous system (ENS). These changes can be found in earliest stages of PD, sometimes years before motor symptoms appear, and therefore have been suggested as a premotor biomarker. Investigating whether high abundance of Prevotellaceae has protective effects against PD or whether low abundance is rather an indicator of disturbed mucosal barrier function will be important. Although very sensitive, low Prevotellaceae levels alone are not specific for PD. Inclusion of other bacterial families may increase accuracy, and further exploring the potential of fecal microbiome analysis as a biomarker for PD seems worthwhile. Further studies may elucidate the temporal and causal relationships between gut microbiota and PD and the mechanisms involved.
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