An OLIP Study (Open Label Individual Patient) of Nusinersen in a Participant With Spinal Muscular Atrophy Who Previously Participated in an Investigational Study With Nusinersen

Inclusion Criteria: 1. Signed informed consent of parent(s) or legal guardian(s) and signed informed assent of the participant, if indicated per participant's capacity to assent and institutional guidelines. 2. Completion of Study 232SM302. 3. Ability to complete all study procedures, measurements, and visits, and parent(s) or legal guardian(s)/participant has adequately supportive psychosocial circumstances, in the opinion of the Investigator. 4. Meets age-appropriate institutional criteria for the use of anesthesia/sedation, if use is planned for study procedures (as assessed by the Investigator and either anesthesiologist or pulmonologist). 5. All female participants of childbearing potential (defined as any female physiologically capable of becoming pregnant) and all male participants of reproductive age must practice effective contraception. Exclusion Criteria: 1. Any new condition or worsening of an existing condition that, according to the Investigator, would make the participant unsuitable for inclusion, could interfere with the assessment of safety, or would compromise the ability of the participant to undergo study procedures. 2. Treatment with another investigational therapy or enrollment in another interventional clinical study after the final dose in Study 232SM302. 3. Treatment with an approved therapy for Spinal Muscular Atrophy after the final dose in Study 232SM302. 4. History of systemic hypersensitivity reaction to nusinersen, the excipients contained in the formulation, and if appropriate, any diagnostic agents to be administered during the study. 5. Participants who are pregnant or currently breastfeeding and those intending to become pregnant during the study. 6. The participant's parent(s) or legal guardian(s) is not willing or able to meet guidelines in the consensus statement for standard of care in Spinal Muscular Atrophy \[Finkel 2018; Mercuri 2018\] or provide nutritional and respiratory support throughout the study, per the Investigator's judgment. 7. Other unspecified reasons that, in the opinion of the Investigator, make the participant unsuitable for enrollment.