A Study to Assess the Safety and Tolerability of Nusinersen (ISIS 396443) in Participants With Spinal Muscular Atrophy (SMA).

The primary objective of Part 1 of this study is to assess the safety and tolerability of Nusinersen in participants with SMA who are not eligible to participate in the clinical studies ISIS 396443-CS3B (NCT02193074) or ISIS 396443-CS4 (NCT02292537). The secondary objective of Part 1 of this study is to examine the pharmacokinetics (PK) of Nusinersen in participants with SMA. The primary objective of Part 2 of this study is to assess the long-term safety and tolerability of Nusinersen in participants with SMA who participated in Part 1 and completed their End of Part 1 Evaluation assessments. The secondary objective of Part 2 of this study is to examine the PK of Nusinersen in participants with SMA who participated in Part 1 and completed their End of Part 1 Evaluation assessments.