Single-Ascending Dose Study of BIIB054 in Healthy Participants and Early Parkinson's Disease

Only healthy participants will be enrolled in Cohorts 1 through 6. Only participants with
early PD will be enrolled in Cohort 7

Key Inclusion Criteria:

1. All women of childbearing potential and all men must practice effective contraception
during the study and for 6 months after their last dose of study treatment.

2. Must have a body mass index from 19 to 32 kg/m2, inclusive.

3. Must be in good health as determined by the Investigator, based on medical history,
physical examination, and 12-lead ECG.

For cohort 7 only:

4. Diagnosis of idiopathic PD

Key Exclusion Criteria:

1. History of cardiovascular disease.

2. Subject smokes more than 5 cigarettes or the equivalent in tobacco daily.

3. Surgery within 3 months prior to Day -1 (other than minor cosmetic surgery and minor
dental surgery, as determined by the Investigator).

4. History or positive test result for hepatitis C, hepatitis B, or human
immunodeficiency virus (HIV).

5. Female subjects who are pregnant, currently breastfeeding, or attempting to conceive
during the study.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.