This study aims to evaluate the impact of the frequency of assessments on the variability over time, reliability, and compliance for the Parkinson's disease (PD) diary in patients with PD in whom medications do not provide adequate control of symptoms.

This is a global, multi-center, noninterventional study of patients with PD aged ≥39 to ≤70 years under standard-of-care treatment that will enroll a minimum of approximately 150 participants and up to 400 participants. Participants will be assigned (1:1) to complete the PD diary either on 3 consecutive days in 1 week (Group A) or 2 consecutive days in each of 2 consecutive weeks (Group B) for a given study visit. During the study, data are collected on motor function, quality of life, and use of PD medications at Baseline and at 3, 6, 12, 18, and 24 months.

Inclusion Criteria

• ≥39 to ≤70 years of age at signing of informed consent
• Diagnosis of clinically established PD as defined by the Movement Disorder Society (MDS) Clinical Diagnostic Criteria for PD
• Marked levodopa responsiveness at screening per investigator's judgment (eg, an estimated ≥30% improvement of MDS-UPDRS Part III score in the off-medication versus on-medication state)
• A minimum of 3 years and a maximum of 10 years from time of PD diagnosis to the date of screening
• Receiving optimized and stable PD medical therapy for ≥1 month prior to screening or demonstrated intolerance to PD medications per investigator's judgment in agreement with the medical monitor
• ≥2 hours of average daily OFF-time assessed within 3 months of screening by PD diary or per investigator's judgment
• Hoehn and Yahr Stage of 1 to 3 while on PD medication assessed within 3 months of screening or at screening
• Normal cognition as determined by the investigator after review of relevant testing (eg, Montreal Cognitive Assessment score of ≥26, or ≥22 if no significant cognitive impairment as determined by neuropsychological testing)

Exclusion Criteria:

• PD with risk of recurrent falls or only tremor-based symptoms
• Diagnosis of primary mitochondrial disorder, epilepsy, stroke, multiple sclerosis, or clinical features suggestive of a neurodegenerative disease other than PD such as Alzheimer's disease
• Any available evidence inconsistent with dopamine deficiency (eg, 18F-DOPA positron emission tomography [PET] or dopamine transporter single-photon emission computed tomography [DAT-SPECT] imaging if performed)
• Moderately severe dyskinesia per investigator's judgment
• Receiving dopamine receptor-blocking agents, including typical neuroleptics, prochlorperazine, and metoclopramide at the time of screening or within 3 months prior to screening
• Treatment with intrajejunal or subcutaneous infusion therapies for PD within 2 months of screening
• History of gene therapy or cell therapy
• Prior surgical or radiation therapy to the brain, including deep brain stimulation and lesion therapy, or prior history of intradural spinal cord surgery
• Receipt of another investigational therapy or device within 2 years of screening unless approved by the medical monitor

Parkinson's disease patients whose medications do not provide adequate control of their symptoms.