A Study to Assess the Efficacy and Safety of Nusinersen (ISIS 396443) in Infants With Spinal Muscular Atrophy

Key Inclusion Criteria:

• Be born (gestational age) between 37 and 42 weeks
• Be medically diagnosed with spinal muscular atrophy (SMA)
• Have Survival Motor Neuron2 (SMN2) Copy number = 2
• Body weight equal to or greater than 3rd percentile for age using appropriatecountry-specific guidelines
• Be able to follow all study procedures
• Reside within approximately 9 hours ground-travel distance from a participating studycenter, for the duration of the study

Key Exclusion Criteria:

• Hypoxemia (oxygen [O2] saturation awake less than 96% or O2 saturation asleep lessthan 96%, without ventilation support) during screening evaluation
• Clinically significant abnormalities in hematology or clinical chemistry parameters orElectrocardiogram (ECG), as assessed by the Site Investigator, at the Screening visitthat would render the participant unsuitable for participation in the study
• Participant's parent or legal guardian is not willing to meet standard of careguidelines (including vaccinations and respiratory syncytial virus prophylaxis ifavailable), nor provide nutritional and respiratory support throughout the study NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.