Early Molecular Biomarkers for Differentiating Parkinsonian Syndromes

Inclusion Criteria: Patients with suspected neurodegenerative parkinsonism in the course of PD or APS, defined according to the 2015 MDS criteria as bradykinesia accompanied by at least one additional symptom: rigidity and/or resting tremor. Age between 40 and 80 years. Written informed consent for participation in the study. Duration of parkinsonian symptoms shorter than 3 years. Abnormal dopamine transporter single-photon emission computed tomography (DaTscan) result confirming presynaptic dopaminergic neuronal degeneration. Exclusion Criteria Lack of consent to participate in the study. Secondary or drug-induced parkinsonism. Other central nervous system (CNS) disorders (e.g., neoplastic or vascular processes) that could account for the symptoms. Active malignancy, infection, or autoimmune inflammatory disease. Severe systemic diseases, including advanced heart failure (New York Heart Association \[NYHA\] class III-IV), poorly controlled diabetes mellitus, renal failure with glomerular filtration rate (GFR) ≤ 60 mL/min/1.73 m², or hepatic failure. Presence of a known monogenic mutation causing parkinsonism according to the Online Mendelian Inheritance in Man (OMIM) classification. Antibiotic therapy or use of probiotics within 3 months prior to the study visit. Pregnancy or breastfeeding.