A Single-Dose, Randomized, Double-Blind, Parallel-Group, Phase 1 Study to Evaluate the Pharmacokinetics, Safety, and Tolerability of BIIB023 in Chinese, Japanese, and Caucasian Adult Healthy Volunteers

Rationale for the Study: Phase 1 pharmacokinetic (PK) data is needed in Chinese and Japanese
populations to support future clinical development of BIIB023 in China and Japan.

Study Design: This is a single-dose study to assess the PK, safety, and tolerability of
BIIB023 administered intravenously (IV) to adult Chinese, Japanese, and Caucasian healthy
volunteers. The Caucasian group is included to allow comparison of PK data from different
groups using data from the same study under the same controlled conditions.

Subjects will be in the clinic for 48 hours around the time of dosing and in the study for up
to 100 days.