This study will assess the safety and efficacy of ATH434 in participants with Multiple System Atrophy

Inclusion Criteria:

1. Participant has clinical features of parkinsonism.
2. Participant has evidence of orthostatic hypotension and/or bladder dysfunction.
3. Participant has ataxia and/or pyramidal signs on neurological examination.
4. Participant is ambulatory.
5. Participant has biomarker evidence of MSA in biologic fluid and on MRI.

Exclusion Criteria:

1. Participant has motor symptoms for > 4 years.
2. Participant has advanced disease, as indicated by frequent falls or choking.
3. Participant has structural brain abnormality on MRI.
4. Participant has any significant neurological disorder other than MSA.
5. Participant has an unstable medical or psychiatric illness.
6. Participant has a contraindication to, or is unable to tolerate, MRI or lumbar puncture.