Looking for blood markers of response to brain surgery

Inclusion Criteria: 1. Diagnosis of "Clinically Established PD" as defined by the Movement Disorder Society Clinical Diagnostic Criteria for Parkinson's disease (MDS-PD criteria) 2. Referred for DBS according to standard local clinical guidelines 2a. Significant motor complications despite optimized pharmacological treatment 2ai. UPDRS motor score \>30/108 in the off-medication state 2aii. Hoehn and Yahr staging \>2.5/5 in the off-medication state 2b. Dopamine responsive 2bi. \>33% improvement in UPDRS motor score after levodopa administration 2c. Age ≤75 years 2d. No contraindication to surgery or other significant comorbidity with limited life expectancy 2e. No significant psychiatric problems or cognitive impairment 2f. No structural lesions or features suggestive of atypical parkinsonism or other mimickers of idiopathic PD on neuroimaging Exclusion Criteria: 1. Unwilling to undergo blood sampling for study purposes 2. Evidence of Parkinsonism due to heavy metal exposure 3. History of neurodevelopmental disorder, neurodegenerative disease other than PD, CNS infection, neuroinflammatory disease (e.g. multiple sclerosis, CNS lupus), malignancy within the last 10 years, cerebrovascular accident, HIV infection, systemic autoimmune disease, alcohol dependence or other substance use 4. Unable to pass DBS pre-operative assessment or unwilling to undergo DBS