Shanghai Clinical Cohort - Parkinson's Disease (Reserve)

* Inclusion Criteria for Clinical PD Group: 1. Patients with a clinical diagnosis of Parkinson's disease (PD) according to the \_Chinese Diagnostic Criteria for Parkinson's Disease (2016 edition)\_. 2. Willingness to undergo biospecimen collection, including cerebrospinal fluid (optional), blood, and saliva, and to complete neuroimaging examinations (MRI, PET/SPECT) and disease-specific clinical assessments. 3. Provision of written informed consent * Inclusion Criteria for Clinical MSA Group: 1. Patients with a clinical diagnosis or clinically probable multiple system atrophy (MSA) according to the Chinese Expert Consensus on the Diagnostic Criteria for MSA (2022). 2. Willingness to undergo biospecimen collection, including cerebrospinal fluid (optional), blood, and saliva, and to complete neuroimaging examinations (MRI, PET/SPECT) and disease-specific clinical assessments. 3. Provision of written informed consent. * Exclusion Criteria for All Participants: 1. Patients with an unclear or uncertain diagnosis. 2. History of stroke, head trauma, hydrocephalus, brain tumor, intracranial hypertension, or intracranial surgery. 3. Evidence of intracranial organic lesions on CT/MRI. 4. Severe anxiety, depression, or schizophrenia. 5. Severe comorbidities involving the heart, lungs, liver, kidneys, endocrine system, or hematological system. 6. Presence of aphasia, severe dysarthria, or other conditions that significantly impair clinical assessments. 7. Anticipated poor compliance.