An Observational Study of Patients With Moderate Parkinson's Disease

Inclusion Criteria: * Male or female, aged 50-68 years (both inclusive) at the time of signing informed consent. * Diagnosed with Parkinson's disease using the Movement Disorder Society (MDS) criteria (fulfilling the definition of clinically probable Parkinson's disease). * Moderate Parkinson's disease, e.g. as defined by i) modified Hoehn and Yahr stage 2-3 in OFF state and ii) MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III total score greater than or equal to (≥) 30 in OFF state, both as judged by the investigator. * Patient has symptoms that are not adequately controlled by existing oral anti-Parkinson's disease medications, i.e., having both ON and OFF periods, as judged by the investigator. * Parkinson's disease duration greater than (\>) 5 years and lesser than or equal to (≤) 12 years from diagnosis at the time of signing informed consent. * Potential candidate for a future cell therapy transplantation, as judged by the investigator. * Life expectancy \>7 years as judged by the investigator. Exclusion Criteria: * Any atypical or secondary Parkinson's disease, or non-Parkinson's disease-suspected cause(s) of, or contributors to, parkinsonism, as judged by the investigator. * Significant drug-induced dyskinesias as judged by the investigator, e.g., as defined by a score of \> 2 in the Abnormal Involuntary Movement Scale (AIMS), in any body part in the ON state. * Tremor-dominant Parkinson's disease, as judged by the investigator. * Cognitive impairment predictive of dementia (including Parkinson's disease dementia) or other cognitive dysfunction as judged by the investigator, e.g., as defined by Montreal Cognitive Assessment (MoCA) score ≤ 24, or evidence of major neurocognitive disorder according to the Diagnostic and Statistical Manual of Mental Disorders V (DSM-V) criteria. * Major medical or psychiatric disorder (e.g., depression (Montgomery-Asberg Depression Rating Scale (MADRS) \>20) or psychosis), or other disease making the patient unsuited for participation in the study, as judged by the investigator. * Treatment for dystonia or spasticity within 3 months of screening (Botox for a focal dystonia is allowed). * Substantial neurological symptoms not accounted for by Parkinson's disease, including active seizure disorder, as judged by the investigator.