Untreated Parkinson's Disease Work-up Assessing Resident Microbiota and Duodenal Barrier Function

\* Inclusion criteria: Patients eligible for inclusion in this study must meet all of the following criteria: 1. Diagnosis of Parkinson's Disease by a neurologist according to the Movement Disorder Society Clinical Diagnostic Criteria for PD 2. Signed informed consent form 3. Aged 18-75 years old 4. Able to understand the study and questionnaires, and comply with study requirements Controls eligible for inclusion in this study must meet all of the following criteria: 1. Aged 40-75 years old 2. Signed informed consent form 3. Able to understand the study and questionnaires, and comply with study requirements * Exclusion criteria: Participants eligible for this study must not meet any of the following criteria: Patients and controls: 1. Gastrointestinal: diagnosis of organic gastrointestinal diseases potentially affecting the assessments during the study (e.g. inflammatory bowel disease (IBD), celiac disease, eosinophilic diseases of the gastro-intestinal tract, gastro-intestinal cancer, diverticulitis in the last 6 months, GI infection in the last 3 months, …). 2. Surgery: major abdominal surgery (including, but not limited to: cholecystectomy, colectomy, hiatal hernia repair, …) except for uncomplicated appendectomy, splenectomy and inguinal hernia repair. 3. Medication use: 1. Any previous exposure to medication used in the treatment of motor symptoms of Parkinson's disease (levodopa, dopamine agonists, MAO-B inhibitors, COMT-inhibitors, NMDA-receptor antagonists, anticholinergics) 2. Antibiotics use in the last 3 months. 3. Use of PPI in the last month. 4. Use of NSAID in the last month. 5. Use of anticoagulation4 (including vitamin K antagonists (VKA), direct oral anticoagulants (DOAC) or low-molecular weight heparins (LMWH)) or dual antiplatelet therapy4 (DUAPT; Acetylsalicilic acid (Asaflow®) + P2Y12-inhibitor (Clopidogrel®)). 4. Pregnancy and breastfeeding. 5. Other: Cancer and/or adjuvant treatment within the last 6 months 6. Exposures: 1. Food intoxication in the last 3 months. 2. Consumptom of more than 2 standard units of alcohol per day. Patients (additional criteria) 1\. Neurological: any major neurological disorder other than Parkinson's disease. Controls (additional criteria) 1. Neurological: 1. A diagnosis of Parkinson's disease or any other major neurological disorder other than Parkinson's disease. 2. Clinical signs of parkinsonism. 3. First degree relative(s) with Parkinson's disease. 2. Gastrointestinal: subjects fulfilling a clinical diagnosis of either Functional dyspepsia, Functional constipation, or Irritable bowel syndrome based on the ROME-IV diagnostic criteria.