This is a Phase 2, double-blind, parallel-group, placebo-controlled study to assess the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy of multiple doses of ONO-2808 in patients with MSA. This is the first study of ONO-2808 in patients with MSA.

This study will consist of a core part, an extension part, and an additional extension part. The purpose of the core part is to evaluate 3 doses of ONO-2808 compared to placebo in MSA patients, including: 1) safety and tolerability, 2) pharmacokinetics, and 3) changes in clinical outcome assessments (COA) and biomarkers considered to be related to the pharmacodynamics and potential efficacy of ONO-2808. The purpose of the extension part and the additional extension part is to evaluate 3 doses of ONO-2808 in MSA patients, including: 1) safety and tolerability and 2) changes in COAs and biomarkers considered to be related to the pharmacodynamics and potential efficacy of ONO-2808.

Inclusion Criteria:

1. Female or male patients with a diagnosis of clinically-established or clinically-probable MSA according to the novel Movement Disorder Society (MDS) criteria for MSA diagnosis (2022), including patients with MSA of either subtype (MSA-P or MSA-C).

2. Patients at the early stages of the disease, defined as a maximum of 5 years since the onset of one of the following symptoms associated with MSA:

   • Parkinsonism
   • Ataxia
   • Orthostatic hypotension and/or urinary dysfunction

3. Patients with an anticipated survival of at least 3 years in the opinion of the Investigator.

4. Patients who are able to ambulate without the assistance of another person, defined as the ability to take at least 10 steps and then to turn around and walk at least another 10 steps. Use of assistive devices (e.g., walker or cane) is allowed.

5. Ability to swallow oral medication and be willing to adhere to the study intervention regimen.

Exclusion Criteria:

1. Pregnant or lactating females.
2. Patients with a clinically-significant or unstable medical or surgical condition other than MSA that, in the opinion of the Investigator, might preclude safe completion of the study or might affect the results of the study (e.g., pulmonary, cardiovascular [including bradyarrhythmia], macular edema, and significant renal or hepatic dysfunction).
3. Neurological diseases/disorders other than MSA, such as Parkinson's disease, dementia with Lewy bodies, essential tremor, progressive supranuclear palsy, spinocerebellar ataxia, spastic paraparesis, corticobasal degeneration, or vascular, normal pressure hydrocephalus, pharmacological, or post-encephalitic parkinsonism.
4. Patients with documented liver diseases or cirrhosis.
5. Positive results at Screening for active viral infections that include positive human immunodeficiency virus (HIV), hepatitis B surface antigen (HBsAg) and hepatitis B core antibody, and hepatitis C virus (HCV).
6. Patients with suicide ideation according to the Investigator's clinical judgment per the Columbia Suicide Severity Rating Scale (C-SSRS) at Screening or who have made a suicide attempt in the 6 months before Screening.