A Study of Nusinersen Among Participants With Spinal Muscular Atrophy Who Received Onasemnogene Abeparvovec

Key Inclusion Criteria:

For all participants:

   - Genetic documentation of 5q SMA homozygous gene survival motor neuron 1 (SMN1)
   deletion or mutation, or compound heterozygous mutation

   - SMN2 copy number of ≥1

   - ≤36 months of age at the time of first Nusinersen dose

   - Must have previously received onasemnogene abeparvovec per the approved label or
   local/regional regulations ≥2 months prior to first Nusinersen dose

   - Must have suboptimal clinical status per the Investigator

Additional Criteria for Subgroups A and B:

   - ≤9 months of age (270 days) at the time of first Nusinersen dose

   - SMN2 copy number of 2

Additional Criteria for Subgroup A:

   - SMA symptom onset ≤4 months (120 days) of age

   - Must have received intravenous (IV) onasemnogene abeparvovec at >6 weeks to ≤6 months
   (43 days to 180 days) of age

   - Must have received IV onasemnogene abeparvovec after SMA symptom onset

Additional Criteria for Subgroup B:

   - Must have received IV onasemnogene abeparvovec at ≤6 weeks (42 days) of age

Key Exclusion Criteria:

For all participants:

   - Prior exposure to Nusinersen

   - Ongoing severe or serious AEs related to onasemnogene abeparvovec

   - Treatment with an investigational drug, biological agent, or device within 30 days or
   5 half-lives of the agent, whichever is longer, prior to study; any prior or current
   treatment with any survival motor neuron 2 (SMN2)-directed splicing modifier; prior
   antisense oligonucleotide treatment or cell transplantation; gene therapy for the
   treatment of SMA other than onasemnogene abeparvovec. Note: treatment with
   onasemnogene abeparvovec as part of an investigational study is allowed

Additional Criteria for Subgroups A and B:

   - Weight-for-age is below the third percentile, based on WHO Child Growth Standards at
   the time of receiving onasemnogene abeparvovec. Adjustments for the gestational weight
   of premature babies enrolled in Subgroups A and B are allowed provided IV onasemnogene
   abeparvovec was dosed per the approved label or per local/regional regulations.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.