An Open-label Study to Assess the Safety and Tolerability of a Single Intrathecal Dose of ISIS 396443 in Patients With Spinal Muscular Atrophy Who Previously Participated in ISIS 396443-CS1

The primary objective of this study is to examine the safety and tolerability of nusinersen (ISIS 396443) administered intrathecally to participants with Spinal Muscular Atrophy (SMA) who previously participated in ISIS 396443-CS1 (NCT02865109). The secondary objective was to examine the plasma pharmacokinetics of a single dose of ISIS 396443 administered intrathecally to participants with SMA who previously participated in ISIS 396443-CS1.